Add .swiftpm folder to default GitIgnore file

[S2Ler]

I noticed that when I use SPM project from Xcode, .swiftpm folder is created. Would be good to ignore it by default.

[BenchR267]

Thanks for this contribution. However, in the .swiftpm directory we store important files like the Package.resolved which we recommend not ignoring in your source control software.
It helps you that all team mates fetch the same version of your dependencies. Also, although we don't commit on anything here, we might use this directory for other important files. It makes sense to have xcuserdata/ in the gitignore but that's already the case.

[S2Ler]

Got it, thanks for clarifications.

[regexident]

@BenchR267 Isn't Package.resolved still generated right next to Package.swift, i.e. not in .swiftpm/?

[BenchR267]

Oh yeah, you're right. But the directory is still used for shared schemes and shouldn't be ignored.