Confirm new rules owing to velocity of ruby / rails releases recently

Author: luke-hill

.github/workflows/build.yml

@@ -10,13 +10,19 @@ jobs:
         ruby: [ '2.5.8', '2.6', '2.7', '3.0', '3.1' ]
         gemfile: [ 'rails_5_0', 'rails_5_1', 'rails_5_2', 'rails_6_0', 'rails_6_1', 'rails_7_0' ]
         exclude:
-          # Only test latest Rails (Of each major), on actively supported Ruby Versions
-          # Only test latest Ruby with latest Rails versions (Of each major)
-          # 2.5  -> Not 5.2/6.1
-          # 2.6  -> Users of this should be using Rails 5.2+
-          # 2.7  -> Users of this should be using Rails 5.2+
-          # 3.0  -> Rails 6.1 and 7.0
-          # 3.1  -> Only 7.0
+          # Newest ruby will test
+          # - all permissible rails versions in latest major
+          # - latest rails version in the last major
+          # Supported rubies will test
+          # - all permissible rails versions in latest major
+          # - all permissible supported rails versions beneath latest major
+          # Unsupported rubies will test
+          # - all permissible rails versions released within 6 months of EOL
+
+          # 2.5 -> Unsupported since March '21 -> Only test up to Sep '21
+          # 2.6 -> Supported until March '22
+          # 2.7 -> Supported until March '23 (At least)
+          # 3.0 -> Supported for a while...
           - { ruby: '2.5.8', gemfile: 'rails_5_2' }
           - { ruby: '2.5.8', gemfile: 'rails_6_1' }
           - { ruby: '2.5.8', gemfile: 'rails_7_0' }