Add .dropboxignore directory to exclude folders without using selective sync

Emma I have to just post, this is becoming a major issue for me. I've been a Dropbox customer for about 10 years now, but because I've stepped more into the development side of things, not having an ignore pattern file is causing all sorts of issues.

You asked for people to explain why this is important:

I already have a script that goes through and sets the ignore flag on `node_modules` folders in my Programming folder. But when switching branches, I will sometimes need to delete `node_modules` and reinstall packages with npm. When this happens, in the few minutes before my automatic script runs, Dropbox tries to sync the folder and I've had a few times where this can cause some serious issues.

Honestly, I can't imagine this is very hard to do. Please ask the development team to prioritize this. I will start my search for an alternative anyway, because I don't have much faith this will get addressed after 98 pages of comments.