doc: recompile before testing core module changes

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: https://github.com/nodejs/io.js/pull/2051
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>