Enable issues for slog-rs/term and slog-rs/envlogger

[MOZGIII]

Both https://github.com/slog-rs/term and https://github.com/slog-rs/envlogger have issues I'd like to report, however issues are disabled for those repos and there's no clear documentation on where to report issues besides the usual GitHub issue tracking locations.
https://github.com/slog-rs/json already have issues enabled, which is confusing.

Both repos state that the issues should reported here, however this issue tracker is not well-organized to support this kind of cross-repo issue tracking. For example, it's not possible to have an overview of the issues specific to just a single sub-repo.

[dpc]

I have troubles checking multiple issue trackers. It's not ideal, but works OKish. Please just report the issues here. :)

[MOZGIII]

Alright, how about we add some guidance on how to report issues in a structured way.

For instance:

When creating an issue, specify the crate name in the beginning of the title: slot-term: need some fix.