rm build folder again;

This was nice to remove a step from the compilation instructions,
but it means that we can't wipe the build directory without causing
git changes.

.gitignore

@@ -1,4 +1,5 @@
 .tup
+build
 /lovr
 /data
 /*.lua

README.md

@@ -86,6 +86,7 @@ Building
 Here's how to compile LÖVR using CMake:
 
 ```console
+mkdir build
 cd build
 cmake ..
 cmake --build .

build/.gitignore

@@ -1 +0,0 @@
-*