Add ep_prompt_for_name to encourage users to use a pseudo/name after 5s

pica-etherpad/Dockerfile

@@ -48,6 +48,7 @@ RUN curl -SL https://github.com/ether/etherpad-lite/archive/${ETHERPAD_VERSION}.
         ep_pad_activity_nofication_in_title \
         ep_pads_stats \
         ep_page_view \
+	ep_prompt_for_name \
         ep_set_title_on_pad \
         ep_subscript_and_superscript \
         ep_tables2 \