Added so the buffer shows info when open

[Kirikmelet]

Before when I called PackerSync or PackerUpdate, I would get an error in display.lua line 388; which reads 'Buffer is not "modifiable"'.

So to fix it, I added api.nvim_buf_set_option(buf, 'modifiable', true) in make_header above the function to get width.

[wbthomason]

Hmm, could you give me more information on your setup? The display window has been working without error for me (and others) for months now, so (unless there's been a breaking change on Neovim HEAD), I'm not sure why you would've seen this issue.

Thanks for the PR, also!

[Kirikmelet]

Sorry, I found the issue I was having, turns out an autogroup I was using to save folds caused the buffer to be set nomodifiable.

Should I close this pull request or should I leave it open?

[wbthomason]

Ah, I'm glad you got things working. Let's close this PR, but if you'd like to make another PR adding a "Troubleshooting" section to the README with this information, that'd be very welcome! No worries if you'd rather not, though.

Thanks!

[Kirikmelet]

Ok