Merge #836: add the community Telegram channel

aa49169a22 add the community Telegram channel (openoms)

Pull request description:

  https://t.me/joinmarketorg has 185 members now with good engagement.
  Admins include @kristapsk and me
  ![image](https://user-images.githubusercontent.com/43343391/111900012-f002b900-8a27-11eb-85bb-e66e09e7e42b.png)

  Telegram needs a phone number to register, but connecting through a proxy (including Tor) is well supported in the desktop app:
  ![image](https://user-images.githubusercontent.com/43343391/111900042-1cb6d080-8a28-11eb-9c5b-247ec65e59c8.png)

  As discussed with @chris-belcher on IRC it wouldd make sense to add it to the readme.

ACKs for top commit:
  AdamISZ:
    ACK aa49169a22 also.
  kristapsk:
    ACK aa49169a22

Tree-SHA512: b127755139d0442ebc5204bde4f78c514223d2749e0530f3e8a7ed1e31c00842958d11cf5037a9db477d4711c00ff4bdab13605dfd002fade8687e6f8535594a

README.md

@@ -106,6 +106,8 @@ Instructions for developers for testing [here](docs/TESTING.md). If you want to
 
 + Twitter: https://twitter.com/joinmarket
 
++ Telegram: https://t.me/joinmarketorg
+
 ### Support JoinMarket and bitcoin privacy
 
 Donate to help make JoinMarket even better: [Obtain a bitcoin address here](https://bitcoinprivacy.me/joinmarket-donations)