docs: Update description of compatible method

Co-authored-by: Robb Kidd <[email protected]>

instrumentation/base/lib/opentelemetry/instrumentation/base.rb

@@ -31,6 +31,11 @@ module Instrumentation
     #         end
     #
     #         # if the target library is present, is it compatible?
+    #         # Common ways to retrieve a gem's version for comparison:
+    #         # - ::Gemname::VERSION if the gem declares a version constant
+    #         # - ::Gemname.version if the gem has provided a version method on the gem class
+    #         # If a VERSION constant or version method are not available, as a fallback you can:
+    #         # - Gem.loaded_specs.fetch('gemname').version - attempt to retrieve the gemspec from the gems currently loaded and use its version
     #         compatible do
     #           Gem::Version.new(Sinatra::VERSION)) > MIN_VERSION
     #         end