Development and contributing guidelines updates

[MisRob]

Summary

• Update contributing guidelines based on some latest discussions and experience
  • Suggest contributors ask for a reasonable amount of issues
  • Add a note on our response times
  • Add "How to connect section"
  • Remove "Kolibri" when possible so that guidelines can be copied/pasted more easily across other repositories
  • Marks important points in bold
  • Minor wording tweaks
• Cleans up the guide on running another Kolibri instance in the developer documentation and adds information about Python version required to run pex files

Reviewer guidance

• Preview CONTRIBUTING.md and its copy in README.md
• Preview "Running another Kolibri instance alongside the development server" page in the developer documentation preview

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0b9.dev0_git.7.g912114d9.pex
Windows Installer (EXE)	kolibri-0.16.0b9.dev0+git.7.g912114d9-unsigned.exe
Debian Package	kolibri_0.16.0b9.dev0+git.7.g912114d9-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0b9.dev0+git.7.g912114d9-0.3.0.dmg
Android Package (APK)	kolibri-0.16.0b9.dev0+git.7.g912114d9-0.1.0-debug.apk
TAR file	kolibri-0.16.0b9.dev0+git.7.g912114d9.tar.gz
WHL file	kolibri-0.16.0b9.dev0+git.7.g912114d9-py2.py3-none-any.whl

[marcellamaki]

this looks great, thank you @MisRob!