diff --git a/Dockerfile b/Dockerfile
index 4aa2738..c62cc3b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -3,6 +3,7 @@ MAINTAINER Netz39 Administrators <admin@netz39.de>
 
 RUN apt-get update \
     && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends --no-install-suggests \
-        mercurial
+        mercurial \
+        telnet
 
 RUN hg clone https://hg.prosody.im/prosody-modules/ /usr/local/lib/prosody-modules
diff --git a/README.md b/README.md
index f16055c..50f21ef 100644
--- a/README.md
+++ b/README.md
@@ -3,3 +3,7 @@
 This is for running [prosody](https://prosody.im/) XMPP server software
 as the [Netz39 Jabber-Server](https://jabber.n39.eu/) and maybe you can
 use it, too?!
+
+Based on more or less official [prosody/prosody-docker](https://github.com/prosody/prosody-docker)
+with ideas from [OpusVL/prosody-docker](https://github.com/OpusVL/prosody-docker) and
+[unclev/prosody-docker-extended](https://github.com/unclev/prosody-docker-extended) …