docs: Update README about ownership

[BigLep]

Make a note about who the owners/maintainers are and where they gather.

This helps fix https://github.com/multiformats/js-multiformats/issues/273

This should be merged after:

• [ ] https://github.com/multiformats/github-mgmt/pull/83
• [x] https://github.com/libp2p/js-libp2p/pull/2082