survey: add large item selection to man-page

Signed-off-by: Jeff Hostetler <jeffhostetler@github.com>

Documentation/git-survey.txt

@@ -64,6 +64,33 @@ only refs for the given options are added.
 	Add custom namespace ('refs/prefetch/') to the set.  This namespace
 	is used by background/nightly 'git maintenance' to prefetch commits.
 
+Large Item Selection
+~~~~~~~~~~~~~~~~~~~~
+
+The following options control the optional display of "large items" under
+various dimensions of scale.  The OID of the largest `n` objects will be
+displayed in reverse sorted order.  For each, `n` defaults to 1.
+
+--commit-parents::
+	Shows the OIDs of the commits with the most parent commits.
+
+--commit-sizes::
+	Shows the OIDs of the largest commits by size in bytes.  This is
+	usually the ones with the largest commit messages.
+
+--tree-entries::
+	Shows the OIDs of the trees with the most number of entries.  These
+	are the directories with the most number of files or subdirectories.
+
+--tree-sizes::
+	Shows the OIDs of the largest trees by size in bytes.  This set
+	will usually be the same as the vector of number of entries unless
+	skewed by very long entry names.
+
+--blob-sizes::
+	Shows the OIDs of the largest blobs by size in bytes.
+
+
 OUTPUT
 ------