[GR-19691] Improve documentation for installing with ruby-build.

PullRequest: truffleruby/1157

Author: eregon

doc/contributor/updating-ruby-installers.md

@@ -52,6 +52,17 @@ cc `@hsbt` in the PR description.
 `rbenv` users which installed `ruby-build` using Homebrew need a new release of
 `ruby-build` to try the new TruffleRuby release.
 
+### Create a Release
+
+Once pushed/merged to master, it's a good idea to create a `ruby-build` release,
+so `ruby-build` Homebrew users can get the new TruffleRuby release too:
+
+```bash
+$ script/release
+```
+
+See [this comment](https://github.com/rbenv/ruby-build/pull/1318#issuecomment-548399571) for details.
+
 ## RVM
 
 There is a script in the repo that does everything needed:

doc/user/ruby-managers.md

@@ -31,6 +31,14 @@ installed as a plugin for [`rbenv`](https://github.com/rbenv/rbenv).
 First, you need to upgrade `ruby-build` to get the latest TruffleRuby
 definition. See [`ruby-build`'s instructions for upgrading](https://github.com/rbenv/ruby-build#upgrading).
 
+On macOS, if `ruby-build` is installed via Homebrew and you do not see the
+[latest TruffleRuby release](https://github.com/oracle/truffleruby/releases),
+you might need to install the HEAD version of `ruby-build` with:
+
+```bash
+$ brew reinstall --HEAD ruby-build
+```
+
 Check the latest available version of TruffleRuby with:
 
 ```bash