docs(contributing): commands to install jest globally

Add commands to install jest globally for running individual tests
ISSUES CLOSED: #775

Author: anshumanv

CONTRIBUTING.md .github/CONTRIBUTING.mdCONTRIBUTING.md renamed to .github/CONTRIBUTING.md

@@ -49,6 +49,8 @@ npm link webpack-cli
 -`BIN_TEST_CASES_GREP=/myCase jest test/BinTestCases.test.js`
 
 * To test a single CLI (other type of) test case:
+- If jest is not installed globally
+-`npm i -g jest`
 -`jest path/to/my-test.js`
 
 * To test linting:
@@ -72,6 +74,8 @@ yarn link webpack-cli
 -`BIN_TEST_CASES_GREP=/myCase jest test/BinTestCases.test.js`
 
 * To test a single CLI (other type of) test case:
+- If jest is not installed globally
+ - `yarn global add jest`
 -`jest path/to/my-test.js`
 
 * To test linting: