Better changelog for fossa snippets removal

[spatten]

Overview

I realized that the changelog saying that the fossa snippets subcommand was being removed was way too terse. I added more information and a link to the documentation for fossa analyze --snippet-scan.

Acceptance criteria

The changelog is better and understandable

Testing plan

Risks

Metrics

References

Add links to any referenced GitHub issues, Zendesk tickets, Jira tickets, Slack threads, etc.

Example:

• ANE-123: Implement X.

Checklist

• I added tests for this PR's change (or explained in the PR description why tests don't make sense).
• If this PR introduced a user-visible change, I added documentation into docs/.
• If this PR added docs, I added links as appropriate to the user manual's ToC in docs/README.ms and gave consideration to how discoverable or not my documentation is.
• If this change is externally visible, I updated Changelog.md. If this PR did not mark a release, I added my changes into an ## Unreleased section at the top.
• If I made changes to .fossa.yml or fossa-deps.{json.yml}, I updated docs/references/files/*.schema.json AND I have updated example files used by fossa init command. You may also need to update these if you have added/removed new dependency type (e.g. pip) or analysis target type (e.g. poetry).
• If I made changes to a subcommand's options, I updated docs/references/subcommands/<subcommand>.md.