Update pig readme

examples/pig/README.txt

@@ -1,7 +1,8 @@
 A Pig storage class that reads all columns from a given ColumnFamily, or writes
 properly formatted results into a ColumnFamily.
 
-Setup:
+Getting Started
+===============
 
 First build and start a Cassandra server with the default
 configuration and set the PIG_HOME and JAVA_HOME environment
@@ -31,7 +32,6 @@ for input and output:
 * PIG_OUTPUT_RPC_PORT : the port thrift is listening on for writing
 * PIG_OUTPUT_PARTITIONER : cluster partitioner for writing
 
-
 Then you can run it like this:
 
 examples/pig$ bin/pig_cassandra -x local example-script.pig
@@ -70,3 +70,18 @@ Which will copy the ColumnFamily.  Note that the destination ColumnFamily must
 already exist for this to work.
 
 See the example in test/ to see how schema is inferred.
+
+Advanced Options
+================
+
+The following environment variables default to false but can be set to true to enable them:
+
+PIG_WIDEROW_INPUT:  this enables loading of rows with many columns without
+                    incurring memory pressure.  All columns will be in a bag and indexes are not
+                    supported.
+
+PIG_USE_SECONDARY:  this allows easy use of secondary indexes within your
+                    script, by appending every index to the schema as 'index_$name', allowing
+                    filtering of loaded rows with a statement like "FILTER rows BY index_color eq
+                    'blue'" if you have an index called 'color' defined.
+