Add GitHub actions CI

[lazappi]

Closes #6

Adds:

• Standard package check action
• Linting action
• Commands for documenting and styling using comments on PRs
  • These could also be replaced with actions that do this automatically, not sure which we prefer?

Doesn't add:

• Test coverage - Need tests to be added first
• README rendering - Didn't find a nice action for this, if we want it can either switch to .Rmd or custom build one
• pkgdown rendering - Need to set up pkgdown first

[rcannood]

LGTM!

These could also be replaced with actions that do this automatically, not sure which we prefer?

I quite like being able to run them as commands!

Test coverage - Need tests to be added first

Fair enough

README rendering - Didn't find a nice action for this, if we want it can either switch to .Rmd or custom build one

I'm happy to add it as a PR command. WDYT? Can pick this up in a separate issue if need be

pkgdown rendering - Need to set up pkgdown first

True!

[rcannood]

Wait no. Can you add something to the CHANGELOG.md? 😬

[rcannood]

LGTM!