Restore projects/CMake/CMakeLists.txt (#5191)

For some reason, #5181 deleted it.
This project is intended to be a simple template to set up a project
consuming raylib with CMake.

projects/CMake/README.md

@@ -0,0 +1,27 @@
+# raylib CMake Project
+
+This provides a base project template which builds with [CMake](https://cmake.org).
+
+## Usage
+
+To compile the example, use one of the following dependending on your build target...
+
+### Desktop
+
+Use the following to build for desktop:
+
+``` bash
+cmake -B build
+cmake --build build
+```
+
+### Web
+
+Compiling for the web requires the [Emscripten SDK](https://emscripten.org/docs/getting_started/downloads.html):
+
+``` bash
+mkdir build
+cd build
+emcmake cmake .. -DPLATFORM=Web -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXECUTABLE_SUFFIX=".html"
+emmake make
+```