Add initial production manual for fiddle.

fiddle/PROD.md

+Fiddle Production Manual
+========================
+
+First make sure you are familar with the design of fiddle by reading the
+[DESIGN](./DESIGN.md) doc.
+
+
+Forcing a build
+---------------
+
+You may need for force a build on the server, say if you accidentally wiped
+the mounted drive, or say fiddle is broken and you need to force it to build
+at HEAD and not wait for that commit to make it into a DEPS rolls.
+
+SSH into `skia-fiddle` and run:
+
+    fiddle_build --force --head --alsologtostderr \
+      --depot_tools=/mnt/pd0/depot_tools \
+      --fiddle_root=/mnt/pd0/fiddle
+
+After that finishes restart fiddle:
+
+    sudo systemctl restart fiddle.service
+
+Or restart Fiddle from the push dashboard.
+
+Debugging fiddle\_secwrap.cpp
+-----------------------------
+
+Highly unlikely to be needed, but if font handling changes, for example, then
+Skia applications may start trying to read new directories or make exciting
+new system calls.
+
+If that happens then uncomment the line:
+
+        TRACE_ALL,
+
+in `fiddle_secwrap.cpp`, then compile and run fiddle\_secwrap locally and then
+run it over the offending exe to determine which calls it is making and then
+add those to the whitelist.
+
+Alerts
+======
+
+Items below here should include target links from alerts.
+
+Fiddle is failing to build <a id=build_fail></a>
+------------------------------------------------
+
+This usually isn't a critical error since Fiddle will only start
+using a build of Skia if it was successfully built, but this should
+be addressed so Fiddle doesn't get too far removed from Skia HEAD.
+
+Search logs for "Failed to build LKGR:" and "Successfully built:".
+
+Fiddle is failing to sync<a id=sync_fail></a>
+------------------------------------------------
+
+This sync is for Fiddle updating a local copy of Skia that's used
+to look up git hashes. The repo is located at /mnt/pd0/fiddle/skia.
+
+Search logs for "Failed to update skia repo".
+
+One easy fix is to SSH into the machine and delete the directory and
+then restart Fiddle, which will rebuild the checkout.