Conduct final Explorer Maintenance QA sweep

[ECWireless]

• Ensure README is up to date (chore: remove mention of Rinkey from README #519 )
• Add PR template (chore: add pull request template #523 )
• Contributor docs (chore: add contribution guide #533 )
• Maintenance practices (chore: add MAINTAINERS.md file #534 )
• Maintenance project board (Explorer - Data Exposure)
• Add versioning (https://github.com/livepeer/explorer/releases/tag/v0.1.0)
• Open tickets based on QA

[ECWireless]

We'll also want to create a PR template for future contributors: https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/creating-a-pull-request-template-for-your-repository

This is a solid candidate to base the PR template off of: #374

[rickstaa]

@ECWireless, for the RFP item on contributor docs, maintenance practices, and issue tracking, you can work closely with @mehrdadmms to align on a clear process and documentation. We can collaborate to make this reusable across other open-source repos in the ecosystem.

For publishing a 6-month feature/bug roadmap, you can present a final demo in a community fireside session, collect input via a survey or direct link to the explorer repo afterwards (open issues and new feature requests), and combine that with advisory board feedback (@mehrdadmms can connect you). This should support publishing a tentative roadmap. I’m also happy to provide input as a community member while OOO.

[rickstaa]

@ECWireless you most likely already planned this in but it would also be great to start versioning the repo after you complete the last rfp items. This allows us to credit contributors in the release notes and improve maintainability.