build: find/link readline for upnpctrl

Change-Id: I8a3adaea1827e79340955a4859ce76f621367888
diff --git a/Dockerfile b/Dockerfile
index b18078a..e11cc36 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -5,7 +5,8 @@
 		nettle-dev \
         cppunit-dev gnutls-dev jsoncpp-dev \
         argon2-dev openssl-dev fmt-dev \
-        http-parser-dev asio-dev msgpack-cxx-dev
+        http-parser-dev asio-dev msgpack-cxx-dev \
+        readline-dev
 
 # Build restinio
 RUN mkdir restinio && cd restinio \