Add auto generated comment to lexer dump

bin/pygments-lexers

@@ -2,6 +2,7 @@
 
 from pygments.lexers import get_all_lexers
 
+print "# AUTOMATICALLY GENERATED BY bin/pygments-lexers"
 print "---"
 
 for name, aliases, filenames, mimetypes in get_all_lexers():

lib/linguist/lexers.yml

@@ -1,3 +1,4 @@
+# AUTOMATICALLY GENERATED BY bin/pygments-lexers
 ---
 - !ruby/struct:Linguist::Lexer
   name: JavaScript+Mako