Use shorter links in README

Author: eregon

README.md

@@ -15,7 +15,7 @@ This action currently supports these versions of MRI, JRuby and TruffleRuby:
 | JRuby | 9.2.9.0 |
 | TruffleRuby  | 19.3.0, 19.3.1 |
 
-See https://github.com/eregon/ruby-install-builder/blob/metadata/versions.json
+See [versions.json](https://github.com/eregon/ruby-install-builder/blob/metadata/versions.json)
 for the always up-to-date list of available Ruby versions.
 
 Note that Ruby 2.3 and the OpenSSL version it needs (1.0.2) are both end-of-life,
@@ -34,8 +34,8 @@ The action works for all [GitHub-hosted runners](https://help.github.com/en/acti
 
 Ruby 2.3, JRuby and TruffleRuby are not yet supported on `windows-latest`.
 
-The prebuilt rubies are generated by https://github.com/eregon/ruby-install-builder
-and on Windows by https://github.com/oneclick/rubyinstaller2.
+The prebuilt rubies are generated by [eregon/ruby-install-builder](https://github.com/eregon/ruby-install-builder)
+and on Windows by [RubyInstaller2](https://github.com/oneclick/rubyinstaller2).
 
 ## Usage