config-plugins: Consistently use "/+doc/" for documentation links

Also replace unnecessarily explicit "refs/heads/master" with "master".

Change-Id: I7bbaf35dce2c2cb5fd159387136edc92e4638fc1
diff --git a/Documentation/config-plugins.txt b/Documentation/config-plugins.txt
index f7823ae..cdb7ec7 100644
--- a/Documentation/config-plugins.txt
+++ b/Documentation/config-plugins.txt
@@ -121,7 +121,7 @@
 
 link:https://gerrit-review.googlesource.com/#/admin/projects/plugins/review-strategy[
 Project] |
-link:https://gerrit.googlesource.com/plugins/review-strategy/+/master/src/main/resources/Documentation/about.md[
+link:https://gerrit.googlesource.com/plugins/review-strategy/+doc/master/src/main/resources/Documentation/about.md[
 Documentation]
 
 [[singleusergroup]]
@@ -475,7 +475,7 @@
 appends `label('Owner-Approval', need(_))` to a provided list.
 
 link:https://gerrit-review.googlesource.com/#/admin/projects/plugins/owners[Project] |
-link:https://gerrit.googlesource.com/plugins/owners/+/refs/heads/master/README.md[Documentation]
+link:https://gerrit.googlesource.com/plugins/owners/+doc/master/README.md[Documentation]
 
 [[project-download-commands]]
 === project-download-commands
@@ -532,7 +532,7 @@
 
 link:https://gerrit-review.googlesource.com/#/admin/projects/plugins/ref-protection[
 Project] |
-link:https://gerrit.googlesource.com/plugins/ref-protection/+/master/src/main/resources/Documentation/about.md[
+link:https://gerrit.googlesource.com/plugins/ref-protection/+doc/master/src/main/resources/Documentation/about.md[
 Documentation]
 
 [[reparent]]