Update building/usage instructions

`README.md` § Getting Started

README.md

@@ -11,6 +11,51 @@
 > so thank you early adopters for beïng prepared to encounter and report segfaults and core dumps 😅.
 
 
+## Getting Started
+
+1. As betaware, only Windows and [RubyInstaller2](https://rubyinstaller.org) __without Devkit__ is tested currently.
+   It also needs [MinGW](https://www.mingw-w64.org) in the `PATH`. Things will go unexpected with the MSYS2 Devkit.
+   * Support for Devkit and Linux are planned, but not for Windows going through WSL
+     (but Linux support means yes for Godot Engine and Ruby both contained in WSL).
+
+2. I might publish this project to RubyGems in the future.
+   For now, download/clone this repo to a consistent place (i.e., not the Downloads folder) and run:
+   ```sh
+   gem install mingw-make
+   gem install rake rake-compiler json
+   rake
+   rake clean # optional, delete leftovers
+   ```
+   If you don’t have [symlink permissions][],
+   consider admin elevation for the `rake` line so the script symlinks Ruby DLLs rather than duplicating them.
+
+3. Copy-paste or symlink `generated/godot_rb.gdextension` in your Godot Project
+   (Unlike nearly all GDExtensions, this one uses absolute paths so multiple projects can share the same install.)
+
+4. Have fun with [_real_ singletons](https://ruby-doc.org/current/syntax/modules_and_classes_rdoc.html#label-Singleton+Classes)! 💎
+   (No ideas on exporting projects currently…)
+
+<details>
+<summary><h4>A couple of reminders for Godot.rb development</h4></summary>
+
+* The [`Rakefile`](Rakefile) is for building, not setting up…
+
+* `bundle install` fails on RubyInstaller no-Devkit because of the `Gemfile` app `steep`’s transitive dependency `ffi`.
+  Gem insists to use the platform-independent version of the `ffi` gem, which doesn’t know about
+ `bin/ruby_builtin_dlls/libffi-8.dll` and must compile `libffi` from scratch with `libffi` own `Makefile`.
+  I’m unable to work around this problem one way or another (`#help-wanted`).
+
+* RubyInstaller Ruby utilizes the new Universal C Runtime, but Godot Engine still uses the old MS VC++ Runtime,
+  for they support (on a best-effort basis) the minority who refuse to upgrade their outdated Windows versions.
+  See [godotengine/godot-proposals#9111][] regarding the situations. Fortunately, while mixing runtimes is unsupported,
+  the only known issue is that Ruby cannot print to console (only `Godot#print` and etc. can).
+
+</details>
+
+[symlink permissions]: https://learn.microsoft.com/windows/security/threat-protection/security-policy-settings/create-symbolic-links
+[godotengine/godot-proposals#9111]: https://github.com/godotengine/godot-proposals/discussions/9111
+
+
 ## Features
 
 ### ☑️️ Current
@@ -29,26 +74,15 @@
 [TBA]
 
 
-## Appendix Docs – [`docs/`](docs/)
-
-* [`Building.md`](docs/dev/Building.md)
-* …
-
-
 ## License
 
 ### [`include/godot/`](include/godot/)
 
 Copyright (c) 2014-present Godot Engine contributors. https://godotengine.org/license/
 
-### Bundled 3rd-party libraries in [`build/`](build/)
-
-#### “`libruby`” – [Ruby](https://www.ruby-lang.org) (“CRuby”)
-Distributing in compliance with [its custom terms](https://github.com/ruby/ruby/blob/HEAD/COPYING#L25-L30)
-
 ### The rest of this project
 
-Copyright 2023 ParadoxV5
+Copyright 2024 ParadoxV5
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.

lib/godot_rb.rb

@@ -0,0 +1,5 @@
+raise NotImplementedError, <<~MSG
+  Godot.rb loads from Godot Engine, not Ruby.
+  Refer to `README.md` § Getting Started on how to add Ruby to your Godot project.
+  Also check out https://github.com/godotengine/godot/pull/72883 on what running Godot Engine from Ruby might look like.  
+MSG