Add examples for autolink plugin

I'm aware that some of these are in the usage list above, but I want to start a list of examples that we share with communities and build it out over time.

README.md

@@ -89,3 +89,17 @@ Below is an example of regexp patterns used for autolinking, modified in the `co
     }
 },
 ```
+
+## Examples
+
+1. Autolinking `Ticket ####:text with alphanumberic characters and spaces` to a ticket link. Use:
+  - Pattern: `(?i)(ticket )(?P<ticket_id>)( : )(?P<ticket_info>.*)`
+  - Template: `(ticket ${ticket_id}:${ticket_info})`
+
+2. Autolinking a link to a GitHub PR to a link with format "pr-repo-id". Use:
+  - Pattern: `https://github\\.com/mattermost/(?P<repo>.+)/pull/(?P<id>\\d+)`
+  - Template: `[pr-${repo}-${id}](https://github.com/mattermost/${repo}/pull/${id})`
+
+3. Using autolinking to create group mentions. Use:
+  - Pattern: `@customgroup*`
+  - Template: `[@customgroup]( \\* @user1 @user2 @user3 \\* )`