Update section on how to know build was run on LUCI

Change-Id: I80a812501aeb3c4d894d687326dac3777b2f54c5
Reviewed-on: https://chromium-review.googlesource.com/c/1318587Reviewed-by: Ryan Tseng <hinoka@chromium.org>
Commit-Queue: Eric Foo <efoo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605596}

docs/luci_migration_faq.md

@@ -90,11 +90,11 @@ main differences to expect are:*
 starts with `/p/chromium/builders/…`
 If the build is still running on Buildbot,
 "buildbot" will still be part of the URL path. Also, in
-the Code Review UI, try-builders running on LUCI are
-shown with a LUCI tag as shown below.*
+the Code Review UI, try-builders on Buildbot is shown
+with a "Buildbot" tag. The default with no tag represents
+a LUCI build.*
 
-![LUCI Code Review UI Tag](images/LUCI-CodeReview-Tag.png
-"linux%5chromium%5rel%5ng is a LUCI builder")
+![LUCI Code Review UI Tag](images/LUCI-CodeReview-Tag.png)
 
 *In some cases, builds on LUCI can also have the
 following URL