Change doc references (#532)

* Change doc references

Together with #531, updating GitHub pages references to those hosted by Swift Package Index.

* Change GitHub Pages reference to Swift Package Index

Author: yim-lee

CHANGELOG.md

@@ -58,7 +58,7 @@ The 1.2.0 release includes contributions from [allevato], [clayellis],
 [compnerd], [d-ronnqvist], [natecook1000], [randomeizer], and [rauhul].
 Thank you!
 
-[arrayparse-docs]: https://apple.github.io/swift-argument-parser/documentation/argumentparser/argumentarrayparsingstrategy
+[arrayparse-docs]: https://swiftpackageindex.com/apple/swift-argument-parser/documentation/argumentparser/argumentarrayparsingstrategy
 
 ---
 

README.md

@@ -72,10 +72,10 @@ For guides, articles, and API documentation see the
 [library's documentation on the Web][docs] or in Xcode.
 
 - [ArgumentParser documentation][docs]
-- [Getting Started with ArgumentParser](https://apple.github.io/swift-argument-parser/documentation/argumentparser/gettingstarted)
-- [`ParsableCommand` documentation](https://apple.github.io/swift-argument-parser/documentation/argumentparser/parsablecommand)
+- [Getting Started with ArgumentParser](https://swiftpackageindex.com/apple/swift-argument-parser/documentation/argumentparser/gettingstarted)
+- [`ParsableCommand` documentation](https://swiftpackageindex.com/apple/swift-argument-parser/documentation/argumentparser/parsablecommand)
 
-[docs]: https://apple.github.io/swift-argument-parser/documentation/argumentparser/
+[docs]: https://swiftpackageindex.com/apple/swift-argument-parser/documentation/argumentparser
 
 #### Examples