Fix broken README documentation links

[mehuljariwala]

Update the README to use the current canonical SwiftPM and PackageDescription documentation URLs.

Motivation:

Fixes #10463.

The README documentation links use the retired docs.swift.org/swiftpm/... routing structure. Those routes now redirect to duplicated paths such as latest/documentation/packagemanagerdocs/packagemanagerdocs and return HTTP 404.

The Getting Started link first loads an HTML redirect page that points to the same broken route, so readers cannot reach the guide from the README.

Modifications:

Updated the four affected README links:

• Getting Started
• Package Manager Docs
• PackageDescription API
• Release notes

Each link now uses its canonical docs.swift.org/latest/documentation/... destination with a trailing slash.

Result:

README visitors are taken directly to the current official Swift documentation instead of a redirect chain ending in a 404 page.

Validation:

Followed each replacement URL with redirects enabled and confirmed HTTP 200 responses:

• https://docs.swift.org/latest/documentation/packagemanagerdocs/gettingstarted/
• https://docs.swift.org/latest/documentation/packagemanagerdocs/
• https://docs.swift.org/latest/documentation/packagedescription/
• https://docs.swift.org/latest/documentation/packagemanagerdocs/releasenotes/

The HTTP checks above validate the link changes. Separately, git diff --check passes as a whitespace/conflict-marker sanity check; it does not validate URLs. No Swift source or generated documentation changed.

[mehuljariwala]

@swift-ci please test self hosted

[owenv]

git diff --check also passes. No Swift source or generated documentation changed

How does this validate these changes? My understanding is that all it does is check for conflict markers and white space issues

[mehuljariwala]

You are right: git diff --check does not validate the URLs. I listed it only as a separate whitespace/conflict-marker sanity check. The actual link validation is the preceding HTTP check: each replacement URL was requested with redirects enabled and returned HTTP 200, while the retired routes redirect to duplicated paths that end in 404. I have clarified that distinction in the PR description.