Add comma to to make the information clear

[atul-shimpi]

http://guides.rubyonrails.org/form_helpers.html

5.2 Dealing with Ajax
Unlike other forms making an asynchronous file upload form is not as simple as providing form_for with remote: true.

Insert comma after 'Unlike other forms.' as shown below
Unlike other forms, making an asynchronous file upload form is not as simple as providing form_for with remote: true.

[rails-bot]

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @eileencodes (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[kaspth]

Thanks! In future documentation changes add [ci skip] to the start of your commit message, that way our CI won't run needlessly 😄

[atul-shimpi]

ok.