Create invitation to journalists to join a press-specific mailing list

[ElenaFdR]

Add to a page that speaks directly to journalists (suggested in the discussion of #52).
This will also relate to other proactive engagement with and celebration of our public exposure:

• offer speakers for conferences or experts for media - like Gitlab's "Know about an amazing event we should be at? We'd love to help you find a speaker" call to action at the bottom of their public events listings (should also be part of Add public Foundation events calendar #39)