Enhance "Making your PR Merge Worthy" section

[pkingstonxyz]

This PR seeks to increase the clarity and scope of the "Making your PR Merge Worthy"
section of the The Ansible Development Cycle page.

It updates the wording of the changelog section to fix some small grammar issues and
includes a link to the RST specification.

This PR also adds a section "Testing PRs" with links to information on Integration and
Unit tests because one of the most common comments on PRs is some variation of "Can you write some tests for this?"

[ansible-documentation-bot]

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[pkingstonxyz]

I'm not sure if tests are required per any official policy, or if there is any
nuance for things that shouldn't include tests.

[webknjaz]

I think cases where tests aren't necessary are obvious to contributors (like sending in a typo fix). We probably shouldn't give them any idea along the lines of "by hey, you can actually ignore this requirement". They'll ask if unsure.

[pkingstonxyz]

Hmm okay, I've rephrased to be more ambiguous but I think a call out to "Hey tests are good" should be included for first time contributors especially.

[pkingstonxyz]

3a2fcd4 only capitalizes some acronyms I have no idea why this is failing.

[oraNod]

3a2fcd4 only capitalizes some acronyms I have no idea why this is failing.

@pkingstonxyz Likely one of those transitive blips that just happen from time to time. The check was fine when I re-ran it so whatever the cause, it was unrelated to your commit.