Add ? as help key, closes #194

autoload/tagbar.vim

@@ -2784,7 +2784,7 @@ endfunction
 " s:PrintHelp() {{{2
 function! s:PrintHelp() abort
     if !g:tagbar_compact && s:short_help
-        silent 0put ='\" Press <F1> for help'
+        silent 0put ='\" Press <F1> or ? for help'
         silent  put _
     elseif !s:short_help
         silent 0put ='\" Tagbar keybindings'

doc/tagbar.txt

@@ -311,7 +311,7 @@ KEY MAPPINGS                                                     *tagbar-keys*
 
 The following mappings are valid in the Tagbar window:
 
-<F1>          Display key mapping help.
+<F1>/?        Display key mapping help.
                 Map option: tagbar_map_help
 <CR>/<Enter>  Jump to the tag under the cursor. Doesn't work for pseudo-tags
               or generic headers.

plugin/tagbar.vim

@@ -101,7 +101,7 @@ let s:keymaps = [
     \ ['togglesort', 's'],
     \ ['zoomwin',    'x'],
     \ ['close',      'q'],
-    \ ['help',       '<F1>'],
+    \ ['help',       ['<F1>', '?']],
 \ ]
 
 for [map, key] in s:keymaps