README link to Provider discussion more user-friendly

Let's make a markdown link so when reading on github, you can go right there.

Author: jrochkind

README.md

@@ -64,7 +64,7 @@ The OAI provider library handles serving local content to other clients. Here's
   end
 ```
 
-See {OAI::Provider} for more details
+See comment docs at top of [OAI::Provider](./lib/oai/provider.rb) for more details, including discussion of the `OAI::Provider::ActiveRecordWrapper` class for quich setup of an OAI provider for an ActiveRecord model class (single database table)
 
 Interactive Harvester
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