Add short description of how to configure Tor.

docs/asb/README.md

@@ -118,3 +118,30 @@ If the ASB has insufficient Monero funds to accept a swap the swap setup is reje
 Note that currently there is no specific error sent back to the CLI for such kind of cases, so a user might not know why the swap execution was rejected.
 Note that there is currently no notification service implemented for low funds.
 The ASB provider has to monitor Monero funds to make sure the ASB still has liquidity.
+
+#### Tor and hidden services
+
+The ASB supports will automatically create a Tor hidden service if the Tor control port can be found.
+By default, the ASB will look for the control port under `localhost:9051`.
+To allow the ASB to create hidden services, enable the control port and authentication in your torrc file.
+Concretely, add these lines:
+
+```
+ControlPort 9051
+CookieAuthentication 1
+CookieAuthFileGroupReadable 1
+```
+
+It is important that the user running the ASB has the correct user rights, i.e. is in the same group as the user running Tor.
+E.g. if running on debian and having Tor install via apt, add your user to the following group:
+`sudo adduser $(whoami) debian-tor`.
+When configured correctly, your ASB will print the created onion addresses:
+
+```bash
+./bin/asb start
+May 01 01:31:27.602  INFO Initialized tracing with level: debug
+...
+May 01 01:32:05.018  INFO Tor found. Setting up hidden service.
+May 01 01:32:07.475  INFO /onion3/z4findrdwtfbpoq64ayjtmxvr52vvxnsynerlenlfkmm52dqxsl4deyd:9939
+May 01 01:32:07.476  INFO /onion3/z4findrdwtfbpoq64ayjtmxvr52vvxnsynerlenlfkmm52dqxsl4deyd:9940
+```