Add documentation for installing package on Debian 11

Changelog

@@ -1,4 +1,6 @@
 
+- UPD: modernize Recorder UI (not the actual Frontend project) (#386)
+
 2022-03-14 version 0.8.8
 - FIX: make secs time_t in otr_strftime() (#375)
 - FIX: inaccurate logo name in manifest and missing image (#372)

README.md

@@ -123,6 +123,8 @@ sudo apt-get install ot-recorder
 
 Debian 9 "Stretch":
 
+- we no longer build for this distribution
+
 using Stretch Mosquitto packages:
 
 ```
@@ -134,6 +136,8 @@ sudo apt-get install ot-recorder
 
 Debian 10 "Buster":
 
+- we no longer build for this distribution
+
 using Buster Mosquitto packages:
 
 ```
@@ -143,6 +147,15 @@ sudo apt-get update
 sudo apt-get install ot-recorder
 ```
 
+Debian 11 "Bullseye":
+
+```
+curl https://raw.githubusercontent.com/owntracks/recorder/master/etc/repo.owntracks.org.gpg.key | sudo apt-key add -
+echo "deb  http://repo.owntracks.org/debian bullseye main" | sudo tee /etc/apt/sources.list.d/owntracks.list > /dev/null
+sudo apt update
+sudo apt install ot-recorder
+```
+
 #### systemd service
 
 The packages we provide have a systemd unit file in `/usr/share/doc/ot-recorder/ot-recorder.service` which you can use to have the Recorder started automatically: