feat: Update closed contribution documentation with new branch

[ADubhlaoich]

Proposed changes

Thanks to some follow up work by @eepifanova, we can now target the main branch for closed content work. This commit updates the documentation to reference the main branch, and also adds specificity of origin and remote when referencing it for clarity.

It also adds missing punctuation, and adjusts spacing in an early paragraph using a line break.

Checklist

Before merging a pull request, run through this checklist and mark each as complete.

• I have read the contributing guidelines
• I have signed the F5 Contributor License Agreement (CLA)
• I have rebased my branch onto main
• I have ensured my PR is targeting the main branch and pulling from my branch from my own fork
• I have ensured that the commit messages adhere to Conventional Commits
• I have ensured that documentation content adheres to the style guide
• If the change involves potentially sensitive changes¹, I have assessed the possible impact
• If applicable, I have added tests that prove my fix is effective or that my feature works
• I have ensured that existing tests pass after adding my changes
• If applicable, I have updated README.md and CHANGELOG.md

Footnotes

1. Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation. Please refer to our style guide for guidance about placeholder content. ↩

[github-actions]

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[eepifanova]

@ADubhlaoich it will be available soon, I'll tell you :)

[mjang]

This line confused me until I realized it's an overview of the commands which follow. So maybe:

Suggested change

	Change back to the origin `main` branch, create a new branch, merge your internal branch and push to origin.
	With the following commands, check out the `main` branch, create a new branch, merge your internal branch, and push the changes to origin.

[ADubhlaoich]

I'm confused what the value add in your edit suggestion is: the sentence is an imperative instruction telling you exactly what to do, then showing you how to do it.

In context, the instruction is juxtaposed with the exact commands to follow in the code block immediately afterwards, and there is only one thing you could possibly be pushing, so all this seems to do is add unnecessary words.

[mjang]

The alternative is to be more precise with the commands, something like:

git checkout main
git checkout -b desired-branch-name
git merge internal/other-branch-name
git push origin main

In any case, based on @eepifanova 's suggestion in Slack, this might all become moot.

[eepifanova]

@ADubhlaoich
I confirm using nginx/internal-docs@main as a source branch for all works on documentation.
The @main branch is the default one - so it's easy and convenient to make new branches in internal-docs
The @main branch is full clone of nginx/documentation@main

Feel free to update documentation ^^