Update Contrib docs to match the new reality

[bajtos]

Contributing to Loopback is targeting our old codebases using ES5, eslint, etc. We need to upgrade these guidelines for our new stack (monorepo, TypeScript, prettier, tslint, etc.)

We need to preserve current docs for people contributing to 3.x version of LoopBack - use some sort of versioning like we have for regular docs.

[bajtos]

IMO, the documentation should explain:

• How to configure VisualStudio code for the best experience and what plugins to install.
  • esbenp.prettier-vscode
  • eg2.tslint
  • Additional plugins I found in my VSCode which we may want to describe too:
    • christian-kohler.path-intellisense (?)
    • eg2.vscode-npm-script (?)
    • christian-kohler.npm-intellisense (?)
• Describe TDD cycle, how to quickly re-run tests (and rebuild the solution)
• Explain commands to run before submitting a pull request (npm test)
• Explain how to reset monorepo after changing branches (maybe npm run clean && npm run bootstrap?)

[bajtos]

How to configure VisualStudio code for the best experience and what plugins to install.

• esbenp.prettier-vscode
• eg2.tslint

See #977

[dhmlau]

@bajtos , any outstanding tasks for this ticket?

[jannyHou]

@dhmlau I think comment #950 (comment) covers the tasks in this issue.

[jannyHou]

I believe the original tasks are already finished in PR #977.
Closing this issue.
Let's create a new issue to discuss updating the contribution page in loopback.io.