Add Edit on Github pages for orgs/datasets

[BryanQuigley]

Credit for this goes to JackGilmore in https://github.com/OpenDataScotland/jkan/commit/641bd10b7abf00a1677ff91cc3ff32f126b26955#diff-45a9a1193a7cfd87edb43c63db091a0737180f026c74dd2c08280e6ced090ab4

[timwis]

Great idea @jackgilmore! Agree it makes sense to have this upstream. Thanks for adding it in @BryanQuigley. Just wanted to flag that there's an alternative way to generate the link that (a) doesn't require users set the repo in _config.yml when installing, and (b) handles cases where gh-pages is not the primary branch.

Jekyll sites built on GitHub pages are built with a set of plugins, including github-metadata, which comes with a liquid helper to generate a github edit link. This lets you do:

<a href="{% github_edit_link %}">Open in GitHub</a>

The only thing is that helper would probably fail to run locally without that gem installed, so we'd need to add the github-pages gem to the Gemfile, which we should have done ages ago, as it provides much greater dev-prod parity.

I've just tested this out locally, and it seems to work, so I'll push it up to save you the trouble. Let me know what you think.

[JackGilmore]

Awesome! Glad this was of help and thanks for passing on that bit of knowledge about an easier way to implement the help link. Think I'll be adding in a PR on our JKAN instance to implement this downstream!