Add GitHub Actions CI

[richelbilderbeek]

Here it is: a Pull Request to add GitHub Actions CI to this repo, which fixes #49 .

You can see the run pass at here. After acceptance of this PR, you can find results here, at the Actions tab.

This is all I did:

• I added a default GitHub Actions script by doing usethis::use_github_actions, output with harmless warnings below.
• I added markdown as a Suggested package in DESCRIPTION. This is needed nowadays when using vignettes

✓ Setting active project to '/home/richel/GitHubs/R-package'
✓ Creating '.github/'
✓ Adding '^\\.github$' to '.Rbuildignore'
✓ Adding '*.html' to '.github/.gitignore'
✓ Creating '.github/workflows/'
✓ Writing '.github/workflows/R-CMD-check.yaml'
• Learn more at <https://github.com/r-lib/actions/blob/master/examples/README.md>
Error: Unsupported GitHub remote configuration: 'fork_upstream_is_not_origin_parent'
* Host = 'https://github.com'
* origin = 'richelbilderbeek/R-package' (can push) = fork of 'project-gen3sis/R-package'
* upstream = <not configured>
* The 'origin' GitHub remote is a fork, but its parent is not configured as the 'upstream' remote.

Read more about the GitHub remote configurations that usethis supports at:
'https://happygitwithr.com/common-remote-setups.html'
Run `rlang::last_error()` to see where the error occurred.

[richelbilderbeek]

I should have worked on develop. I will close this PR and create a new fresh one :-)

[richelbilderbeek]

Reopened as @florianhartig thinks that pushing to main is fine. I agree with his line of reasoning.

Note that having a CONTRIBUTING.md file would have taught me to push to develop.

[florianhartig]

Looks fine to me! Good idea with the contributing.md!

[florianhartig]

Many thanks, Richel!

[richelbilderbeek]

@florianhartig thanks so much for accepting that help, from my experience, that is quite rare!

[richelbilderbeek]

@florianhartig are we good to merge this? This is just a friendly reminder: sometimes I forget to push the big green 'Merge' button myself as well :-)

[florianhartig]

I wanted to let @benj919 or @ohagen merge, I just gave my opinion that it looks good to me!