Add template parameters information.

templates/songbook.tmpl

@@ -22,6 +22,22 @@
 % Modified to serve personnal purposes. Newer versions can be 
 % obtained from http://www.lohrun.net.
 
+% Template optionnal parameters (to be read by songbook-client)
+% template mandatory parameter are currently booktype, template and songs
+% the first two have default values but not last one
+%%:{"parameters" : [
+%%:  {"name":"title", "description":"Title", "type":"string"},
+%%:  {"name":"author", "description":"Author", "type":"string", "default":"Alexandre"},
+%%:  {"name":"version", "description":"Version", "type":"string", "default":"1"},
+%%:  {"name":"subtitle", "description":"Subtitle", "type":"string"},
+%%:  {"name":"mail", "description":"Email", "type":"string"},
+%%:  {"name":"picture", "description":"Picture", "type":"string"},
+%%:  {"name":"picturecopyright", "description":"Copyright", "type":"string"},
+%%:  {"name":"footer", "description":"Footer", "type":"string"},
+%%:  {"name":"license", "description":"License", "type":"string"}
+%%:  ]
+%%:}
+
 % template variables
 \providecommand{\template}{}
 \providecommand{\songslist}{}