Update CONTRIBUTING.md

Co-authored-by: Christoph Knittel <christoph@knittel.cc>

Author: cometkim

CONTRIBUTING.md

@@ -57,7 +57,7 @@ opam switch create 5.3.0
 opam install . --deps-only --with-test --with-dev-setup -y
 ```
 
-#### npm install
+#### Install npm packages
 
 Run `yarn install`. This will install the npm dependencies required for the build scripts.