CI: Add Fedora builds (#144)

[lexa]

Add Github actions for building SwayNotificationCenter on every push and publish it on Copr when it is released.

fedora-build.yml builds the package locally on every commit and PR. It is mostly to check that the build is not broken and there is not missing dependencies.

fedora-copr.yml is triggered when SwayNotificationCenter is released. It will start build on the copr. Copr will build the project for different Fedora versions and architectures (x86, arm64, etc).

To make fedora-copr.yml work you need to :

1. Get an account on the copr
2. Create a new project there, lets call it SwayNotificationCenter
3. Set repo secret COPR_REPO_NAME to SwayNotificationCenter (same as project name on Copr)
4. Get a token from https://copr.fedorainfracloud.org/api/ and set it in the repo's secrets as 'COPR_API_TOKEN'.

After that, copr shoud be updated when the next release is done.

I see that you don't want to use Github releases, feel free to change trigger event of fedora-copr.yml to

on:  
  push:
    tags:
      - '*'

[ErikReider]

Cool! Thanks :)

[ErikReider]

Oh. Forgot about updating the README. I'll fix it :)