/subscribe to newsletter + slack

[jsolovjo]

subscribe.markdown file created

[carlad]

once #30 is merged we need to add

{% include edit_on_github.html %}

to the page (I can do this)

[shushugah]

This is good, however I hope we can rename the Slack before this goes live. So will need to pause this. Also inside _config.yml we should add this to the header_links array, so that it shows up in the head.

[jsolovjo]

Do you mean to do like this in _config.yml file?

header_pages:
  - about.markdown
  - events.markdown
  - subsribe.markdown

[ferbsx]

related to #17