doc: recompile before testing core module changes

Changes to core modules do not take effect unless recompiled. Tip new
contributors about this when describing how to run tests in
contribution guide.

Removed `jslint` from first test command example, as jslint is included
when running `make test`.

Fixed wrong path of example stream2-transform test.

PR-URL: #2051
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

CONTRIBUTING.md

@@ -126,7 +126,7 @@ test/parallel/ directory.  Look at other tests to see how they should be
 structured (license boilerplate, common includes, etc.).
 
 ```text
-$ make jslint test
+$ ./configure && make -j8 test
 ```
 
 Make sure the linter is happy and that all tests pass.  Please, do not submit
@@ -142,9 +142,11 @@ $ python tools/test.py -v --mode=release parallel/test-stream2-transform
 You can run tests directly with iojs:
 
 ```text
-$ iojs ./test/parallel/test-streams2-transform.js
+$ ./iojs ./test/parallel/test-stream2-transform.js
 ```
 
+Remember to recompile with `make -j8` in between test runs if you change
+core modules.
 
 ### Step 6: Push