installation docs

book/src/ruby/installation.md

@@ -1,5 +1,33 @@
 # Installation
 
+## Ruby
+
+To build `bevy_scriptum` with Ruby support a Ruby installation is needed to be
+present on your development machine.
+
+The easiest way to produce a compatible Ruby installation is to use [rbenv](https://rbenv.org/).
+
+After installing `rbenv` along with its `ruby-build` plugin you can build and
+install a Ruby installation that will work with `bevy_scriptum` by executing:
+
+```sh
+CC=clang rbenv install 3.4.4
+```
+
+Above assumes that you also have `clang` installed on your system.
+For `clang` installation instruction consult your
+Linux distribution or [clang official webiste](https://clang.llvm.org).
+
+If you rather not use `rbenv` you are free to supply your own installation of
+Ruby provided the following is true about it:
+
+- it is compiled with `clang`
+- it is compiled as a static library
+- it is accessible as `ruby` within `PATH` or `RUBY` environment variable is set
+  to path of desired `ruby` binary.
+
+## Main Library
+
 Add the following to your `Cargo.toml`:
 
 ```toml