Add supported versions policy (#2742)

Author: andyw8

jekyll/supported_versions.markdown

@@ -0,0 +1,15 @@
+---
+layout: default
+title: Supported Versions Policy
+nav_order: 60
+---
+
+# Supported Versions Policy
+
+For Ruby, we support the versions [listed as being under normal maintenance](https://www.ruby-lang.org/en/downloads/branches/).
+
+For Ruby on Rails, we support the versions [listed as supported for bug fixes](https://rubyonrails.org/maintenance).
+
+This means that new features may not be available to older versions, but we still try to ensure that the Ruby LSP is stable.
+
+We will consider contributions to support other versions of these tools, as long as they not detrimental to the project's overall health.