Add documentation for actions-@plugin@.config file

The information is scattered around about how to write an
actions-@plugin@.config file for its-jira. Add it to the
official documentation for easy and centralized accessibility.

Change-Id: Ia9748d0496dca9aa9a2e305a21bc258307d665f4
diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index 3eff578..5864b75 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -134,3 +134,37 @@
            optional
     Issue-id enforced in commit message [MANDATORY/?]: suggested
 
+**Sample actions-@Plugin@.config:**
+
+    [rule "open"]
+        event-type = patchset-created
+        action = add-velocity-comment inline Change ${its.formatLink($changeUrl)} is created.
+        action = In Progress
+    [rule "resolve"]
+        event-type = comment-added
+        approval-Code-Review = 2
+        action = add-velocity-comment inline Change ${its.formatLink($changeUrl)} is verified.
+        action = In Review
+    [rule "merged"]
+        event-type = change-merged
+        action = add-velocity-comment inline Change ${its.formatLink($changeUrl)} is merged.
+        action = Done
+    [rule "abandoned"]
+        event-type = change-abandoned'
+        action = add-velocity-comment inline Change ${its.formatLink($changeUrl)} is abandoned.
+        action = To Do
+
+The first rule triggers an action which adds a comment and a hyperlink to the change created
+in gerrit. The comment will appear in an Jira issue's `Comment` section whenever a patchset-created event
+is triggered. The second action item in the first rule transitions the state of the issue
+in Jira to `In Progress`. The title of the action `In Progress` should match the workflow actions
+used by the JIRA server as different versions of JIRA can have different workflow actions.
+
+**Note:** Velocity comments were deprecated in Gerrit 2.14 and will be removed in Gerrit 2.16/3.0;
+the `actions-@Plugin@.config` needs to be changed accordingly. For example, to use Soy comments instead
+of velocity comments:
+
+    [rule "open"]
+        event-type = patchset-created
+        action = add-soy-comment Change ${its.formatLink($changeUrl)} is created.
+        action = In Progress