Add instructions about updating local Cemu repo

BUILD.md

@@ -57,3 +57,9 @@ You can use it by replacing the step 3 with the following:
  - If step 4 gives you an error that contains something like `main.cpp.o: in function 'std::__cxx11::basic_string...`, you likely are experiencing a clang-14 issue. This can only be fixed by either lowering the clang version or using GCC, see below.
  - If step 4 gives you a different error, you could report it to this repo or try using GCC. Just make sure your standard library and compilers are updated since Cemu uses a lot of modern features!
 - If step 4 gives you undefined libdecor_xx, you are likely experiencing an issue with sdl2 package that comes with vcpkg. Delete sdl2 from vcpkg.json in source file and recompile
+
+## Updating Cemu version
+1. To update your Cemu local repository, use the command `git pull --recurse-submodules`
+ - This should update your local copy of Cemu and all of its dependencies
+2. Then, you can rebuild Cemu using the steps listed above, acording to your Operating System (OS)
+If cmake complains about Cemu already being compiled and similar, try deleting the `CMakeCache.txt` file on the `build` folder.