Dtspo 15970 caching (#465)

* DTSPO-15970 - updating caching documentation

* change formatting

* spell check

* added 429 to ignore

Rakefile

@@ -9,7 +9,7 @@ task :check_urls do
         {
             :check_external_hash => false,
             :ignore_missing_alt => true,
-            :ignore_status_codes => [0, 401, 403],
+            :ignore_status_codes => [0, 401, 403, 429],
             :ignore_urls =>  [
                 # Ignore pulls/branches as these do not translate to raw content
                 %r{github\.com/hmcts/(?=.*(?:pull|tree|commit))},