Launch Plan: The PostHog Pyramid Scheme

Let's finish the referral program feature set we did at the hackathon.

Best practices

[x] Ensure the product has at least one customer story within 3 weeks of launch (@joethreepwood will write about our usage) - https://github.com/PostHog/posthog.com/pull/8462
[x] Ensure we publish best practice content for the product and link to it from docs (@joethreepwood will cover this) - https://github.com/PostHog/posthog.com/pull/8462
[ ] Ensure that products have at least one pre-made template (or similar) for users (@raquelmsmith unsure if we need this?)
[x] Ensure the product has at least one tutorial at launch (@joethreepwood will cover this in the marketing PR) - https://github.com/PostHog/posthog.com/pull/8462
[x] Ensure the product has a robust docs page, and product page if needed - https://github.com/PostHog/posthog.com/pull/8462

The following items have to be completed before launch, taken from the Pyramid Scheme channel on Slack.

[x] Finish up the referrer page
[ ] Add the ability to add/edit referrers and redeemers
[ ] Make referral links work when directing to posthog.com (not us or eu instances)
[ ] Sort out the event sending
[ ] Trigger the tracking event on sign-up
[ ] Trigger tracking event somehow when someone pays their first bill

Stretch goals for the future:

[ ] Make API to get all redeemers for a given referrer for any program in the current team
[ ] Track referral attribution with posthog-js (not in a custom cookie)
[ ] Manually create referrer
[ ] Verify referral code (via search)
[ ] Referral code customization
[ ] Redeem the code via posthog-js
[ ] Program analytics (referrals over time, shares, etc)
[ ] Embeddable components for referral widgets
[ ] Link sharing attribution
[ ] Shopify integration
[ ] Stripe integration

Below will all be done by @joethreepwood, unless otherwise stated.

[x] Key art by @lottiecoxon - https://github.com/PostHog/posthog.com/issues/8476
[ ] Announce on changelog
[ ] Announce in changelog newsletter
[ ] Announce in PostHog for Startups newsletter
[ ] Announce with Pylon broadcast to all users
[ ] Add to Product OS page - https://github.com/PostHog/posthog.com/pull/8462
[ ] Add to onboarding email flow

All feedback and additional ideas from @PostHog/marketing is appreciated.