Fix build instructions (#1701)

Summary:
This change fixes a missing step (cd) in the build instructions.

Pull Request resolved: #1701

Reviewed By: sryap

Differential Revision: D45011147

Pulled By: q10

fbshipit-source-id: 704ce5bd3cfbd62c31f434c830a7300e5d645024

README.md

@@ -42,7 +42,7 @@ cd build
 cmake -DUSE_SANITIZER=address -DFBGEMM_LIBRARY_TYPE=shared -DPYTHON_EXECUTABLE=/usr/bin/python3 ..
 
 # Run the build
-make -C build -j VERBOSE=1
+make -j VERBOSE=1
 
 # Run all tests
 make test