doc: fix broken sentence

Also, the move was done nearly a year ago

Author: tshepang

src/test/COMPILER_TESTS.md

@@ -1,4 +1,4 @@
 # Compiler Test Documentation
 
-Documentation the compiler testing framework has moved to
+Documentation for the compiler testing framework can be found in
 [the rustc guide](https://rust-lang.github.io/rustc-guide/tests/intro.html).