mapping manager documentation

Author: Ihar Yakimush

README.md

@@ -54,7 +54,7 @@ IQueryable<Product> solrLinq = solr.AsQueryable(setup =>
     // override default serializer if needed
     options.SolrFieldSerializer = new DefaultFieldSerializer();
 
-	// override default mapping manager if needed
+    // override default mapping manager if needed
     options.MappingManager = new AttributesMappingManager();
 });
 ```