Move build instructions to BUILDING.md

this is all handled by Github Actions so we probably don't need this anymore but it's good to keep around

BUILDING.md

@@ -0,0 +1,16 @@
+ ### Windows
+ 1. Open Visual Studio 2019 and clone this repository
+ 2. The default configuration should be "x86-Release" for the 32bit version\
+ If you want the 64bit version select the "x64-Release" configuration
+ 3. Select `Build` -> `Build All`
+ 4. The .dll should now be in `gmod-discord-rpc/cpp/build/\*-Release/`
+
+ ### Linux
+ 1. Make sure you have git, cmake, and gcc installed
+ 2. Open a terminal and run
+ ```git clone https://github.com/fluffy-servers/gmod-discord-rpc --recursive
+ cd gmod-discord-rpc/cpp
+ mkdir build && cd build
+ cmake .. && cmake --build .
+ ```
+ 3. The .dll should now be in `gmod-discord-rpc/cpp/build/`