Doc: add missing tags for g:startify_list_order

Closes #187.

doc/startify.txt

@@ -134,22 +134,21 @@ At the moment startify supports these lists:~
 1) "files"
 
    This lists the most recently used files using viminfo. The number of files
-   is limited by g:startify_files_number.
+   is limited by |g:startify_files_number|.
 
 2) "dir"
 
    This lists the files from the current directory sorted by modification
-   time. The number of files is limited by g:startify_files_number.
+   time. The number of files is limited by |g:startify_files_number|.
 
 3) "bookmarks"
 
    This lists bookmarks, thus hardcoded files or directories that will always
-   be shown. Have a look at g:startify_bookmarks.
+   be shown. Have a look at |g:startify_bookmarks|.
 
 4) "sessions"
 
-   This lists all the sessions saved in the directory
-   g:startify_session_dir.
+   This lists all the sessions saved in the directory |g:startify_session_dir|.
 
 Section headers:~