Add compile_commands.json documentation for C/C++ (#22639)

Added documentation explaining that clangd requires
`compile_commands.json` for proper functionality in both C and C++
projects. Includes instructions for generating the file using CMake.

This is related to
https://github.com/zed-industries/zed/discussions/6480

Release Notes:

- N/A

---------

Co-authored-by: Peter Tripp <peter@zed.dev>

docs/src/languages/c.md

@@ -49,3 +49,17 @@ You can trigger formatting via {#kb editor::Format} or the `editor: format` acti
 ```
 
 See [Clang-Format Style Options](https://clang.llvm.org/docs/ClangFormatStyleOptions.html) for a complete list of options.
+
+## Compile Commands
+
+For some projects Clangd requires a `compile_commands.json` file to properly analyze your project. This file contains the compilation database that tells clangd how your project should be built.
+
+### CMake Compile Commands
+
+With CMake, you can generate `compile_commands.json` automatically by adding the following line to your `CMakeLists.txt`:
+
+```cmake
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+```
+
+After building your project, CMake will generate the `compile_commands.json` file in the build directory and clangd will automatically pick it up.

docs/src/languages/cpp.md

@@ -98,3 +98,17 @@ Diagnostics:
 ```
 
 For more advanced usage of clangd configuration file, take a look into their [official page](https://clangd.llvm.org/config.html).
+
+## Compile Commands
+
+For some projects Clangd requires a `compile_commands.json` file to properly analyze your project. This file contains the compilation database that tells clangd how your project should be built.
+
+### CMake Compile Commands
+
+With CMake, you can generate `compile_commands.json` automatically by adding the following line to your `CMakeLists.txt`:
+
+```cmake
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+```
+
+After building your project, CMake will generate the `compile_commands.json` file in the build directory and clangd will automatically pick it up.