Update clang update docs.

- mention chromium.clang tot waterfall
- linux cfi bot is now on luci

Bug: 731417
Change-Id: I01b4b01ac35741f66a63f23af78a09d9c1e83495
Reviewed-on: https://chromium-review.googlesource.com/1237113Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592894}

docs/updating_clang.md

 # Updating clang
 
+1.  Check that https://ci.chromium.org/p/chromium/g/chromium.clang/console
+    looks reasonably green.
 1.  Sync your Chromium tree to the latest revision to pick up any plugin
     changes
 1.  Run `python tools/clang/scripts/upload_revision.py NNNN`
@@ -40,9 +42,9 @@
 
     ```shell
     git cl try &&
-    git cl try -m tryserver.chromium.linux -b linux_chromium_cfi_rel_ng &&
     git cl try -m tryserver.blink -b linux_trusty_blink_rel &&
     git cl try -B luci.chromium.try -b ios-device -b mac_chromium_asan_rel_ng \
+      -b linux_chromium_cfi_rel_ng \
       -b linux_chromium_chromeos_asan_rel_ng -b linux_chromium_msan_rel_ng \
       -b linux_chromium_chromeos_msan_rel_ng -b linux-chromeos-dbg
     ```