Feature summary (what you would like to be able to do and where):
Add a filter to .gitignore for Pywikibot so that .swp files are ignored

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
While trying to use vim to edit several files and fix a bug, I noticed that git status showed all the .swp files that vim creates while you have an existing file open for editing. This makes the output of git status cluttered, and risks the addition of the wrong files to a patch.

Benefits (why should this be implemented?):
.gitignore is created to help ignore files that have no place in version control, and .swp files are exactly that.