Merge bitcoin/bitcoin#35400: doc: Remove good_first_issue.yml, Reword "Getting started" section

fa51f37f18 doc: Reword the Getting-Started section (MarcoFalke)
fab5733f5d doc: Remove good_first_issue.yml (MarcoFalke)

Pull request description:

  Fixes https://github.com/bitcoin/bitcoin/issues/35399

  IIUC, the good-first-issue label and template were meant to make it easier for completely new contributors to get started with something simple. However, I don't think the label and issue template are applicable anymore:

  * There are currently no issues with this label, and directing people toward an empty list seems pointless.
  * Historically the issue and label has been used rarely. 2026: once, 2025 twice, 2024 thrice. Source: https://github.com/bitcoin/bitcoin/issues?q=state%3Aclosed%20is%3Aissue%20label%3A%22good%20first%20issue%22
  * The template has been mis-used, according to https://github.com/bitcoin/bitcoin/issues/35399

  Fix all issues by removing it, since it is clear that it is no longer actively used, nor applicable and possibly a net-negative overall.

  Of course, regular devs are still free to open issues of this kind as a normal issue, if they wish. However, having the template for this in this repo and tracking it via a label doesn't seem useful.

  Since removing the template and label requires rewriting the "Getting Started" section in  `CONTRIBUTING.md`, I went ahead and also removed the mention of `Up for grabs` as good things for newcomers to work on. I don't recall the last new contributor that picked something up successfully. Also, `Up for grabs` is usually stuff that people lost interest in, or is no longer relevant.

  Instead I've added a sentence to encourage new contributors to help with critical and broad review, which will naturally guide them to good first follow-up issues to work on.

  Meta: I know this topic can be subjective and offer bike-shed potential, but I am happy to iterate a bit on this for a few days.

ACKs for top commit:
  stickies-v:
    ACK fa51f37f18
  danielabrozzoni:
    ACK fa51f37f18
  sedited:
    ACK fa51f37f18
  darosior:
    ACK fa51f37f18
  furszy:
    ACK fa51f37f18
  winterrdog:
    ACK fa51f37f18

Tree-SHA512: 9e6d7fe86262bee2df1e0af33ecfb5f77036da2d5d1832bb6afb08f4107d9313eec06d8b769966bf8ecaf8a4c574da5ff99509cc4b7fd9c53ea86788da29721c

.github/ISSUE_TEMPLATE/good_first_issue.yml

@@ -1,44 +0,0 @@
-name: Good First Issue
-description: (Regular devs only) Suggest a new good first issue
-labels: [good first issue]
-body:
-  - type: markdown
-    attributes:
-      value: |
-        Please add the label "good first issue" manually before or after opening
-
-        A good first issue is an uncontroversial issue, that has a relatively unique and obvious solution
-
-        Motivate the issue and explain the solution briefly
-  - type: textarea
-    id: motivation
-    attributes:
-      label: Motivation
-      description: Motivate the issue
-    validations:
-      required: true
-  - type: textarea
-    id: solution
-    attributes:
-      label: Possible solution
-      description: Describe a possible solution
-    validations:
-      required: false
-  - type: textarea
-    id: useful-skills
-    attributes:
-      label: Useful Skills
-      description: For example, “`std::thread`”, “Qt6 GUI and async GUI design” or “basic understanding of Bitcoin mining and the Bitcoin Core RPC interface”.
-      value: |
-        * Compiling Bitcoin Core from source
-        * Running the C++ unit tests and the Python functional tests
-        * ...
-  - type: textarea
-    attributes:
-      label: Guidance for new contributors
-      description: Please leave this to automatically add the footer for new contributors
-      value: |
-        Want to work on this issue?
-
-        For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.
-

CONTRIBUTING.md

@@ -19,38 +19,18 @@ Getting Started
 
 New contributors are very welcome and needed.
 
-Reviewing and testing is highly valued and the most effective way you can contribute
-as a new contributor. It also will teach you much more about the code and
-process than opening pull requests. Please refer to the [peer review](#peer-review)
-section below.
+In-depth reviewing and testing are the bottleneck of the project, and are the
+most effective way anyone can start to contribute. It will teach you much more
+about the code and process than opening pull requests, and may help you uncover
+related issues and follow-ups to contribute code for. Please refer to the [peer
+review](#peer-review) section below.
 
 Before you start contributing, familiarize yourself with the Bitcoin Core build
 system and tests. Refer to the documentation in the repository on how to build
 Bitcoin Core and how to run the unit tests, functional tests, and fuzz tests.
 
-There are many open issues of varying difficulty waiting to be fixed.
-If you're looking for somewhere to start contributing, check out the
-[good first issue](https://github.com/bitcoin/bitcoin/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22)
-list or changes that are
-[up for grabs](https://github.com/bitcoin/bitcoin/issues?utf8=%E2%9C%93&q=label%3A%22Up+for+grabs%22).
-Some of them might no longer be applicable. So if you are interested, but
-unsure, you might want to leave a comment on the issue first.
-
 You may also participate in the [Bitcoin Core PR Review Club](https://bitcoincore.reviews/).
 
-### Good First Issue Label
-
-The purpose of the `good first issue` label is to highlight which issues are
-suitable for a new contributor without a deep understanding of the codebase.
-
-However, good first issues can be solved by anyone. If they remain unsolved
-for a longer time, a frequent contributor might address them.
-
-You do not need to request permission to start working on an issue. However,
-you are encouraged to leave a comment if you are planning to work on it. This
-will help other contributors monitor which issues are actively being addressed
-and is also an effective way to request assistance if and when you need it.
-
 Communication Channels
 ----------------------