Documents how to handle new ruby versions.

docs/NEW_RUBIES.md

@@ -0,0 +1,13 @@
+# Handling New Ruby Versions
+
+When a new Ruby version comes out, you shouldn't have to make any immediate changes to StandardRb. The default configuration is the `base.yml` configuration and should continue to work correctly.
+
+Often, Rubocop will add new rules to encourage usage of new language features in new Ruby versions. When that happens:
+
+1. Add the rule to the base.yml file and disable it.
+1. Assess the new rule and see if it should be added to StandardRb. If not, you're done. If so, enable in `base.yml` and read on.
+1. Add a new config file for the penultimate minor version of Ruby, so for example, if the new Ruby version is `3.1` then the new config file would be for `3.0`.
+1. In the new config file, make sure it inherits from `base.yml` and disable the new rule.
+1. In the previous latest config file, make sure it inherits from your new config file.
+
+And that should add new rules to StandardRb safely and gracefully.