automatic deployment for PRs

[alifeee]

it nearly works

it works fine on this repository (on the staging-deployment-works-internally tag) for internal PRs

it does not work yet for pull requests from forks, as these are funky

I need to set this up actions/checkout#518 (comment) so that an action can both

• use the code from the forked PR (with pull_request event)
• use the secrets from this repository (with pull_request_target event)

(this is not something that github actions likes you doing)

alternatively, I could just tell forks that they should create their own secrets for surge and it will work for them

also, the surge step doesn't fail if the ENV variables SURGE_LOGIN and SURGE_KEY are unset. It should, then it would be obvious that it fails.

This sounds like a good compromise, and the action could report the URL in the same way that github pages reports the URL as an output

[alifeee]

could write surge description in a contirbuting guide

[alifeee]

done, final commit is in 5ee5ff9

[alifeee]

it just uses comments, not deployments, because there is no ref to use if the pull request comes from a fork