Improve documentation about the self-hosted input

* Fixes #535

README.md

@@ -263,6 +263,9 @@ In other cases, you will need to install Ruby in the runner tool cache as shown
 (run it so it will show you where to install Ruby).
 You could of course also not use this action and e.g. use Ruby from a system package or use a Docker image instead.
 
+See also the [`self-hosted:` input](action.yml).
+You can set it to `true` if you want to use custom-built Rubies in your self-hosted toolcache instead of prebuild Rubies.
+
 ## History
 
 This action used to be at `eregon/use-ruby-action` and was moved to the `ruby` organization.

action.yml

@@ -34,7 +34,7 @@ inputs:
     description: |
       Consider the runner as a self-hosted runner, which means not using prebuilt Ruby binaries which only work
       on GitHub-hosted runners or self-hosted runners with a very similar image to the ones used by GitHub runners.
-      The default is to detect this automatically based on the OS, OS version and $RUNNER_TOOL_CACHE.
+      The default is to detect this automatically based on the OS, OS version and architecture.
 outputs:
   ruby-prefix:
     description: 'The prefix of the installed ruby'

common.js

@@ -173,7 +173,7 @@ const GitHubHostedPlatforms = [
   'windows-2022-x64',
 ]
 
-// Actually a self-hosted runner for which  the OS and OS version does not correspond to a GitHub-hosted runner image,
+// Actually a self-hosted runner for which the OS and OS version does not correspond to a GitHub-hosted runner image,
 export function isSelfHostedRunner() {
   if (inputs.selfHosted === undefined) {
     throw new Error('inputs.selfHosted should have been already set')