docs: added writing changeset docs

[nikkimk]

Description

• Added writing-changesets.md to our Guides.
• Linked to writing-changesets.md from .changesets/README.md.
• Linked to writing-changesets.md from ./README.md.

Motivation and context

We need to provide guidance for writing good changesets. We should make the distinction between commits and changesets clear: Commits are for a contributor audience. Changesets are for a consumer audience.

Related issue(s)

• resolves SWC-826

Screenshots (if appropriate)

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Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed at the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my changes. (N/A this is a docs PR)
• I have included a well-written changeset if my change needs to be published.
• I have included updated documentation if my change required it.

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Reviewer's checklist

• Includes a Github Issue with appropriate flag or Jira ticket number without a link
• Includes thoughtfully written changeset if changes suggested include patch, minor, or major features (N/A this is a docs PR)
• Automated tests cover all use cases and follow best practices for writing (N/A this is a docs PR)
• Validated on all supported browsers
• All VRTs are approved before author can update Golden Hash

Manual review test cases

• Writing changesets guide

  1. Go to the Writing changesets guide
  2. Review the docs
  3. Suggest edits

• Links to the guide

  1. Review the changes to the changesets readme
  2. Review the changes to our repo's readme
  3. Suggest edits

Device review

• Did it pass in Desktop?
• Did it pass in (emulated) Mobile?
• Did it pass in (emulated) iPad?

[changeset-bot]

⚠️ No Changeset found

Latest commit: 9f2e58c

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

[github-actions]

Branch preview

• Documentation Site
• Storybook

Review the following VRT differences

When a visual regression test fails (or has previously failed while working on this branch), its results can be found in the following URLs:

• Spectrum | Light | Medium | LTR
• Spectrum | Dark | Large | RTL
• Express | Light | Medium | LTR
• Express | Dark | Large | RTL
• Spectrum-two | Light | Medium | LTR
• Spectrum-two | Dark | Large | RTL
• High Contrast Mode | Medium | LTR

If the changes are expected, update the current_golden_images_cache hash in the circleci config to accept the new images. Instructions are included in that file.
If the changes are unexpected, you can investigate the cause of the differences and update the code accordingly.

[github-actions]

Tachometer results

Currently, no packages are changed by this PR...

[blunteshwar]

This looks great!