Document release process

[vmx]

Create a document similar to https://github.com/libp2p/js-libp2p/blob/40739e96398fe5715068f5ecb12a5b973c172e2b/RELEASE.md that describes the release process.

This issue is related to #136.

[vmx]

Also make sure it's announced on the forum (see ipfs/js-ipfs#1765 for more information).