Suggest adding a .gitattributes file

[Calvin-L]

While working on sublimehq/package_control_channel#8090, I was surprised
to learn that there is a way to exclude files from the final package.

[FichteFoll]

While I don't know whether we want to suggest this as a general way around such issues, it should definitely mention that this affects all types of archives you create for a git repo, including from the command line and all sorts of archives downloadable from github.

It is definitely a solution for some, but I wouldn't feel good just suggesting the option without its downsides.

[Calvin-L]

Thanks for pointing that out; I've amended the text to note the potential downsides.

Perhaps this PR should be rejected, and something else should be added to the docs. Now that I understand this a little better, it seems like there is a real use case for some mechanism that

• excludes files from the packages distributed to end-users, but
• does not affect developer activities like downloading release archives from GitHub.

Does such a mechanism exist? I don't see one mentioned anywhere.