Updated Compiling (markdown)

Compiling.md

@@ -61,6 +61,18 @@ Optional:
 - minizip
 - zlib
 
+Check out SPIRV-Cross: *(Optional for slang shader support)*
+
+SPIRV-Cross is a submodule located in the main source directory at `shaders/SPIRV-Cross`. If you are using a git clone, you can simply run:
+```
+snes9x$ git submodule update --init shaders/SPIRV-Cross
+```
+If you are using a tarball, but have git installed, you can run:
+```
+snes9x$ git init && git submodule update --init shaders/SPIRV-Cross
+```
+Otherwise, you will need to place the SPIRV-Cross source files in the `shaders/SPIRV-Cross` directory manually.
+
 Building with meson:
 1. Change to the `gtk` directory and run meson:
 ```