docs(gulpfile): Getting started, Further reading, About gulpfile.js

Add documentation to gulpfile.litcoffee:
- Tech stack
- Preparing workspace
- Building the project
- Further readind (refer to source/index.litcoffee)
- About gulpfile.js
fix(gulpfile): run only test files ending with .test.litcoffee

This allows to create .litcoffee non-test files like fixtures.