Make buffer readonly again

This time we pay more attention to when the buffer will still be written by the
plugin itself.

Note to self: Never commit after midnight.

autoload/startify.vim

@@ -53,6 +53,7 @@ function! startify#insane_in_the_membrane() abort
 
   silent! setlocal
         \ bufhidden=wipe
+        \ colorcolumn=
         \ nobuflisted
         \ nocursorcolumn
         \ nocursorline
@@ -61,7 +62,6 @@ function! startify#insane_in_the_membrane() abort
         \ norelativenumber
         \ nospell
         \ noswapfile
-        \ colorcolumn=
   if empty(&statusline)
     setlocal statusline=\ startify
   endif
@@ -152,7 +152,7 @@ function! startify#insane_in_the_membrane() abort
   autocmd startify CursorMoved <buffer> call s:set_cursor()
 
   silent! file Startify
-  set filetype=startify
+  set filetype=startify readonly
   if exists('#User#Startified')
     if v:version > 703 || v:version == 703 && has('patch442')
       doautocmd <nomodeline> User Startified
@@ -765,7 +765,7 @@ function! s:set_mark(type, ...) abort
         \ 'T': 'tabnew',
         \ }
 
-  setlocal modifiable
+  setlocal noreadonly modifiable
 
   if entry.marked && index[0] == a:type
     let entry.cmd = 'edit'
@@ -779,7 +779,7 @@ function! s:set_mark(type, ...) abort
     execute 'normal! ci]'. repeat(a:type, len(index))
   endif
 
-  setlocal nomodifiable nomodified
+  setlocal readonly nomodifiable nomodified
 endfunction
 
 " Function: s:sort_by_tick {{{1