Changes to readme and contributor guide

Value

Hope to make contribution details clearer to avoid MR's sitting unnoticed and to ensure folks have a checklist they can refer to before making an MR to ensure they have run test etc. Also a chance to make any other small updates or improvements to the two docs.

Implementation Notes

Add the contributor guide link at to the top of the readme file as well as where it is now.

• Under "Hi! This is mainly..." add something like "If you would like to contribute to Signalboost please read https://0xacab.org/team-friendo/signalboost/blob/master/CONTRIBUTING.md"

Add a point form summary/checklist to the contributor guide.

• Possibly even above the table of contents something that is as point form as possible. eg:
  • Read the Code of Conduct and this guide.
  • Contact us if you've got questions, we are friendly.
  • Open a feature or bug report issue for your code so we can support you.
  • Use your issue id in your branch and commits eg: 99-add-lollipops-branch / "[99] adds the red pops commit"
  • Please rebase in master before you create a Merge Request, we prefer rebase to merge.
  • Please write or extend tests.
  • Please use ES6 style JS and features: https://ponyfoo.com/articles/es6
  • Run our tests before submitting a Merge Request (using make test.all) this will also run a lint.
  • Make a Merge Request and tag either @aguestuser or @fdbk -- we will try to review as soon as we can.
• ....then where each of those links to the appropriate section of the guide.