Add new Docs source files (#8461)

docs/source/building.md

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+# Building
+
+## Building with CMake
+
+The distribution main build system is configured by
+[`cmake`](https://www.cmake.org) which allows you to build the project for any
+platform.
+
+### Configuration
+
+Use `cmake` to configure a project based on your environment and platform.
+
+=== "Unix"
+
+    ```sh
+    cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release
+    ```
+
+    !!! note
+
+        To use `clang` instead of `gcc` you may need to set prepend some
+        environment variables e.g. `CC=/usr/bin/clang CXX=/usr/bin/clang++ cmake
+        -G "Unix MakeFiles"`
+
+=== "Windows"
+
+    ```sh
+    cmake -G "Visual Studio 17 2022" -DCMAKE_BUILD_TYPE=Release
+    ```
+
+=== "MacOS"
+
+    ```sh
+    cmake -G "Xcode" -DCMAKE_BUILD_TYPE=Release
+    ```
+
+### Building
+
+Once the project files are generated, build as normal for your platform.
+
+=== "Unix"
+
+    ```sh
+    make flatc
+    ```
+
+=== "Windows"
+
+    ```sh
+    msbuild.exe FlatBuffers.sln
+    ```
+
+## Building with Bazel
+
+## Building with VCPKG