Write very basic OUTPUT section for pt-upgrade.

bin/pt-upgrade

@@ -11354,7 +11354,54 @@ will read from C<STDIN>.
 
 =head1 OUTPUT
 
-TODO
+Queries are group by fingerprints and any with differences are printed.
+The first part of a query report is a summary of differences.  In the example
+below, the query returns a different number of rows (C<row counts>) on
+each server.  The second part is the side-by-side comparison of values
+obtained from the query on each server.  Then a sample of the query is
+printed, preceded by its ID which can be used to locate more information
+in the sub-report at the end.  There are sub-reports for various types of
+differences.
+
+  # Query 1: ID 0x3C830E3839B916D7 at byte 0 _______________________________
+  # Found 1 differences in 1 samples:
+  #   column counts   0
+  #   column types    0
+  #   column values   0
+  #   row counts      1
+  #   warning counts  0
+  #   warning levels  0
+  #   warnings        0
+  #            127.1:12345 127.1:12348
+  # Errors               0           0
+  # Warnings             0           0
+  # Query_time                        
+  #   sum                0           0
+  #   min                0           0
+  #   max                0           0
+  #   avg                0           0
+  #   pct_95             0           0
+  #   stddev             0           0
+  #   median             0           0
+  # row_count                         
+  #   sum                4           3
+  #   min                4           3
+  #   max                4           3
+  #   avg                4           3
+  #   pct_95             4           3
+  #   stddev             0           0
+  #   median             4           3
+  use `test`;
+  select i from t where i is not null
+
+  /* 3C830E3839B916D7-1 */ select i from t where i is not null
+
+  # Row count differences
+  # Query ID           127.1:12345 127.1:12348
+  # ================== =========== ===========
+  # 3C830E3839B916D7-1           4           3
+
+The output will vary slightly depending on which options are specified.
 
 =head1 OPTIONS