docs: Add info on using blamer to the sheriffing docs.

site/dev/sheriffing/index.md

 Tree Sheriffs Documentation
 ===========================
 
 ### Contents ###
 
 *   [What does a sheriff do?](#what_is_a_sheriff)
     +   [Skia tree](#skia_tree)
     +   [DEPS rolls](#deps_rolls)
     +   [Gold and Perf](#gold_and_perf)
     +   [Documentation](#sheriff_doc)
@@ skipping 13 matching lines @@
 -----------------------
 
 A sheriff keeps an eye on the tree, DEPS rolls, Gold tool and the Perf tool.
 
 Below is a brief summary of what the sheriff does for each task:
 
 <a name="skia_tree"></a>
 ### Skia tree
 * Understand the [buildbots infrastructure](https://skia.org/dev/testing/buildbot).
 * Start watching the [status page](https://status.skia.org) for bot breakages.
-* Track down people responsible for breakages and revert broken changes if there is no easy fix.
+* Track down people responsible for breakages and revert broken changes if there is no easy fix. You can use [blamer](#blamer) to help track down such changes.
 * Close and open the [tree](http://skia-tree-status.appspot.com).
 * Keep the builder comments on the [status page](https://status.skia.org) up to date.
 * File or follow up with [BreakingTheBuildbots bugs](https://bug.skia.org/?q=label:BreakingTheBuildbots). See the tip on [when to file bugs](#when_to_file_bugs).
 
+<a name="blamer"></a>
+### Blamer
+If you have Go installed, a command-line tool is available to search through
+git history and do text searches on the full patch text and the commit
+message. To install blamer run:
+
+    go get go.skia.org/infra/blamer/go/blamer
+
+Then run blamer from within a Skia checkout. For example, to search if the
+string "SkDevice" has appeared in the last 10 commits:
+
+    $ $GOPATH/bin/blamer --match SkDevice --num 10
+
+    commit ea70c4bb22394c8dcc29a369d3422a2b8f3b3e80
+    Author: robertphillips <robertphillips@google.com>
+    Date:   Wed Jul 20 08:54:31 2016 -0700
+
+        Remove SkDevice::accessRenderTarget virtual
+        GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2167723002
+
+        Review-Url: https://codereview.chromium.org/2167723002
+
 <a name="deps_rolls"></a>
 ### DEPS rolls
 * Ensure that [AutoRoll Bot](https://autoroll.skia.org)'s DEPS rolls land successfully.
 
 <a name="gold_and_perf"></a>
 ### Gold and Perf
 * Pay attention for new [Perf](https://perf.skia.org/) and [Gold](https://gold.skia.org/) alerts (by clicking on the bell at the top right of the [status page](https://status.skia.org)).
 * The sheriff's duty here is to make sure that when developers introduce new images or new perf regressions, that they are aware of what happened, and they use these tools to take appropriate action.
 
 <a name="sheriff_doc"></a>
@@ skipping 103 matching lines @@
   * Add # comment about what has changed
   * Add line(s) like the following after the comment:
       * crbug.com/<bug#youjustcreated> foo/bar/test-name.html [ NeedsRebaseline ]
         * (if you took the second option above you can just edit the existing line(s))
 
 * If you took the first/dispreferred option above:
   * Wait for the Blink patch to roll into Chrome
   * Create a Chrome patch that removes your suppressions from skia/skia_test_expectations.txt