Add supported Ruby versions and deprecate "sudo gem install" to system Ruby

[ainame]

Closes #1018

Last year Ruby 3.0 was released and I started working on Ruby 3.0 migration project lately. I realised that not a few people pick up Ruby 3.0 as their first Ruby version to install and get errors. fastlane/fastlane#17931

Right now if you try gem install fastlane with Ruby 3.0, it results in getting version "2.54.1", which is too old. We've gotten several issues due to that. To clarify supported versions, I updated the installation guide page.

And also there is something bugging me always, which is recommending using "sudo". It's almost common sense among Ruby developers, which we should avoid using system's Ruby and should adopt some manager solution for local Ruby environment. So I tried updating that part as well.

I know Ruby environment for mobile app developers is not as important as for web developers but wanted to stop recommending system Ruby + "sudo" at least, which makes us even harder to track GitHub issues; e.g. fastlane/fastlane#15183 (comment)

In addition, Apple clearly mentioned that macOS won't include Ruby in future. We will need to admit this anyway.

Scripting language runtimes such as Python, Ruby, and Perl are included in macOS for compatibility with legacy software. Future versions of macOS won’t include scripting language runtimes by default, and might require you to install additional packages. If your software depends on scripting languages, it’s recommended that you bundle the runtime within the app. (49764202)

https://developer.apple.com/documentation/macos-release-notes/macos-catalina-10_15-release-notes

[rogerluan]

Really welcome changes! Left some copy improvements, links and some feedback you might want to consider 😊

Thanks for this ❤️

[ainame]

@rogerluan Took all your suggestions and removed unnecessary whitespace🙂 Thank you for the review!

[rogerluan]

Good stuff!! Cheers 🎉

[ainame]

We'll then need to replace inline messages in fastlane itself as well🙂
https://github.com/fastlane/fastlane/search?q=sudo+install

[rogerluan]

Oh boy ☝️ 😅

[joshdholtz]

This is a much needed change! Thanks for making this 😊

I added two small change requests to change the vibe of the sentences a little bit so let me know what you think!

Feel free to merge this on your own when ready 😊

[ainame]

@joshdholtz Thank you very much for your review! I just applied your suggestions so, please ♻️

Requested changes were applied.

[rogerluan]

@ainame from Josh's last message I think he meant we can merge once those changes were applied 🎉 . netlify is failing to build this PR for some reason though 🤔 should we investigate that, or was it failing before as well?

[rogerluan]

Josh's suggestions were 💯 😁

[rogerluan]

Looks like the netlify issue is also present in master 😬 we can probably just merge this in then AFAIC

[joshdholtz]

Yeah, Netlify isn't super important but I should look into that 😊 I think I have access to that account somewhere 😬

But merge away!

Click 👏 that 👏 button 👏

[ainame]

Ah sorry, I thought Josh requested change too. I'm going to merge this now and will work on the "sudo" instructions in code next 👍