doc: Regroup clang-tidy rules

* Remove the explicit modernize-use-nullptr rule mention, which has not been needed for years.
* Encourage devs to refer to the upstream clang-tidy rules documentation.
* Move NOLINTNEXTLINE(misc-no-recursion) into a subsection under the new clang-tidy section.

doc/developer-notes.md

@@ -55,7 +55,6 @@ code.
 
 - **Miscellaneous**
   - `++i` is preferred over `i++`.
-  - `nullptr` is preferred over `NULL` or `(void*)0`.
   - `static_assert` is preferred over `assert` where possible. Generally; compile-time checking is preferred over run-time checking.
   - Use a named cast or functional cast, not a C-Style cast. When casting
     between integer types, use functional casts such as `int(x)` or `int{x}`
@@ -63,8 +62,6 @@ code.
     Use `reinterpret_cast` and `const_cast` as appropriate.
   - Prefer [`list initialization ({})`](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#res-list) where possible.
     For example `int x{0};` instead of `int x = 0;` or `int x(0);`
-  - Recursion is checked by clang-tidy and thus must be made explicit. Use
-    `NOLINTNEXTLINE(misc-no-recursion)` to suppress the check.
 
 For function calls a namespace should be specified explicitly, unless such functions have been declared within it.
 Otherwise, [argument-dependent lookup](https://en.cppreference.com/w/cpp/language/adl), also known as ADL, could be
@@ -140,7 +137,18 @@ public:
   non-optional in-out and output parameters should usually be references, as
   they cannot be null.
 
-### Coding Style (C++ named arguments)
+### Coding Style (clang-tidy rules)
+
+The clang-tidy tool is used to check some rules. Please refer to the [upstream
+documentation](https://clang.llvm.org/extra/clang-tidy/checks/list.html) about
+the details and rationale for each rule.
+
+#### C++ Recursive Functions
+
+Recursion is checked by clang-tidy and thus must be made explicit. Use
+`NOLINTNEXTLINE(misc-no-recursion)` to suppress the check.
+
+#### C++ named arguments
 
 When passing named arguments, use a format that clang-tidy understands. The
 argument names can otherwise not be verified by clang-tidy.
@@ -156,7 +164,7 @@ int main()
 }
 ```
 
-### Running clang-tidy
+#### Running clang-tidy
 
 To run clang-tidy on Ubuntu/Debian, install the dependencies: