Update More Info link for `Building from Source` section

[ParadoxV5]

Commit c00feff removed the How to compile and install section from the main README.md, possibly in favour of the separate building_ruby.md page.

The More Info link Building from Source section of the Installation webpage (e.g.: en page) still points to the removed header. It should be updated to link to building_ruby.md, either:

• from the master branch on GitHub: https://github.com/ruby/ruby/blob/master/doc/contributing/building_ruby.md
• hosted on docs.ruby-lang.org: https://docs.ruby-lang.org/en/master/contributing/building_ruby_md.html
• ~~hosted on ruby-doc.org~~ Looks like this one is still hosting the version as released with Ruby 3.1.2 whose README.md do have the How to compile and install section: https://ruby-doc.org/core-3.1.2/README_md.html#label-How+to+compile+and+install