some additional documentation about rewrite strategies

app/logical/downloads/rewrite_strategies/base.rb

@@ -1,3 +1,7 @@
+# This is a collection of strategies for normalizing URLs. Most strategies 
+# typically work by parsing and rewriting the URL itself, but some strategies 
+# may delegate to Sources::Strategies to obtain a more canonical URL.
+
 module Downloads
   module RewriteStrategies
     class Base

app/logical/sources/strategies/base.rb

@@ -1,3 +1,11 @@
+# This is a collection of strategies for extracting information about a 
+# resource. At a minimum it tries to extract the artist name and a canonical 
+# URL to download the image from. But it can also be used to normalize a URL 
+# for use with the artist finder. It differs from Downloads::RewriteStrategies
+# in that the latter is more for normalizing and rewriting a URL until it is 
+# suitable for downloading, whereas Sources::Strategies is more for meta-data 
+# that can only be obtained by downloading and parsing the resource.
+
 module Sources
   module Strategies
     class Base