docs: remove alpha branch chapter from README

[franklanganke]

New Pull Request Checklist

• I am not disclosing a vulnerability.
• I am creating this PR in reference to an issue.

Issue Description

Update default branch name

Related issue: #1422

Approach

• update readme.md

TODOs before merging

• Add changes to documentation (guides, repository pages, in-code descriptions)

[parse-github-assistant]

Thanks for opening this pull request!

• 🎉 We are excited about your hands-on contribution!

[mtrezza]

Thanks for pointing this out! I am not sure whether we want to keep that paragraph at all. We now have 2 branches (alpha, release) + in the future maybe beta + N LTS branches (release-N.x.x). To explain only the alpha branch seems a bit arbitrary. We actually have a better branch explanation in the changelog already, which is likely more prominent than that last paragraph in the README.

To avoid keeping redundant info that has to maintained separately, I suggest we just remove the whole paragraph (and the TOC entry).

[mtrezza]

Looks good!

[codecov]

Codecov Report

Merging #1430 (c3037fb) into alpha (a2026d3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            alpha    #1430   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          61       61           
  Lines        5948     5948           
  Branches     1354     1354           
=======================================
  Hits         5945     5945           
  Misses          3        3           

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[parseplatformorg]

🎉 This change has been released in version 3.4.0-alpha.3

[parseplatformorg]

🎉 This change has been released in version 3.4.1