Adding the following to NotificationAgents.xml allows Telegram to work for notifications. Not the easiest process to setup though. First you have to send @BotFather a message '/newbot', after a few steps it sends you back your HTTP API. Then you need to start a conversation with your bot in order to get the Chat ID to send to. Not sure there is an easy way to integrate this into the settings page, I manually queried the API to get the chat ID.
<Agent>
<Name>Telegram</Name>
<Variables>
<Variable Help="The API key can be found [a href='https://core.telegram.org/bots/api' target='_blank'] [u]here[/u].[/a]" Desc="API key" Default="">API_KEY</Variable>
<Variable Help="Chat ID [a href='https://core.telegram.org/bots/api' target='_blank'] [u]here[/u].[/a]" Desc="Chat ID" Default="">CHAT_ID</Variable>
<Variable Help="Specify the fields which are included in the message body of the notification." Desc="Notification Message" Default="$DESCRIPTION">MESSAGE</Variable>
</Variables>
<Script>
<![CDATA[
#!/bin/bash
##########
{0}
##########
MESSAGE=$(echo -e "$MESSAGE")
URL=https://api.telegram.org/bot$(echo -e "$API_KEY")
CHATID=$(echo -e "$CHAT_ID")
curl -s -k -G \
--data-urlencode "text=$MESSAGE" \
$URL/sendMessage?chat_id=$CHATID
]]>
</Script>
</Agent>
Edit: While looking for something else I noticed theres another way to get the chatid. Send '/getid' to IDBot @myidbot (https://telegram.me/myidbot) and it will reply with your chat id