Added comment regarding the officially endorsed Erlang debian repository

Author: Roberto Quintanilla

Dockerfile

@@ -3,6 +3,10 @@ FROM debian:wheezy
 # add our user and group first to make sure their IDs get assigned consistently, regardless of whatever dependencies get added
 RUN groupadd -r rabbitmq && useradd -r -d /var/lib/rabbitmq -m -g rabbitmq rabbitmq
 
+# Add the officially endorsed Erlang debian repository:
+# See:
+#  - http://www.erlang.org/download.html
+#  - https://www.erlang-solutions.com/downloads/download-erlang-otp
 RUN apt-key adv --keyserver pool.sks-keyservers.net --recv-keys 434975BD900CCBE4F7EE1B1ED208507CA14F4FCA
 RUN echo 'deb http://packages.erlang-solutions.com/debian wheezy contrib' > /etc/apt/sources.list.d/erlang.list