man: add a note about the visrc.lua structure to vis.1

As seen in #669 I didn't *get it* one needs to have a special stub in
`visrc.lua` for everything to work properly. Putting at least a few
words in the man page might help some others like me in the future :)

Close #671

1 files changed, 5 insertions, 0 deletions

diff --git a/man/vis.1 b/man/vis.1
index 9f5ec89..dfae8ca 100644
--- a/man/vis.1
+++ b/man/vis.1
@@ -1509,6 +1509,11 @@ or
 depending on the build configuration.
 .El
 .
+.Pp
+When creating a new
+.Pa visrc.lua
+be sure to copy the structure from here.
+.
 .Sh EXIT STATUS
 .
 .Ex -std