Add docs for creating beta releases

[rygine]

Summary

• Updated the contributing guide to outline the steps necessary for creating a beta release

[cloudflare-pages[bot]]

Deploying xmtp-js-docs with    Cloudflare Pages

Latest commit:	b9a48bb
Status:	✅  Deploy successful!
Preview URL:	https://8fbb5774.xmtp-js.pages.dev
Branch Preview URL:	https://rygine-beta-release-docs.xmtp-js.pages.dev

View logs

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: b9a48bb139ad4b6d974cc75fc9305283c0d14e90

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR