[script] Add generation of english posters

.gitignore

@@ -7,7 +7,10 @@ poster.html
 poster.pdf
 poster_light.png
 poster_dark.png
+poster_light_en.png
+poster_dark_en.png
 poster.txt
+poster_en.txt
 http.access.log
 http.error.log
 events.ical
@@ -16,4 +19,4 @@ events.html
 events_archive.html
 
 
-!site/lif*
+!site/lif*