doc: make the message visible (#3837)
doc: make the message visible (#3837)

[doc]

RTD needs that to render the text.
Oncilla/scion,netsec-ethz/scion,Oncilla/scion,Oncilla/scion,netsec-ethz/scion,Oncilla/scion,netsec-ethz/scion,netsec-ethz/scion