Document fallback code owners in user guide

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I60e9b13cc273e5a46ef2a77bb485f98af3126f8a

resources/Documentation/user-guide.md

diff --git a/resources/Documentation/user-guide.md b/resources/Documentation/user-guide.md
index 6e31243..1471348 100644
--- a/resources/Documentation/user-guide.md
+++ b/resources/Documentation/user-guide.md
@@ -146,8 +146,10 @@
 
 If the code owners functionality is enabled, all touched files require an
 approval from a code owner. If files are touched for which no code owners are
-defined, the change can only be submitted with a [code owner
-override](#codeOwnerOverride).
+defined, the change can only be submitted with an approval of a fallback code
+owner (if [configured](config.html#pluginCodeOwnersFallbackCodeOwners)) or with
+a [code owner override](#codeOwnerOverride). Please note that fallback code
+owners are not included in the [code owner suggestion](#codeOwnerSuggestion).
 
 If the destination branch doesn't contain any [code owner config
 file](#codeOwnerConfigFiles) at all yet and the project also doesn't have a