fix(llms.txt): remove stale invite-required note

Invite gating was already turned off a while back; sign-up is open to
everyone now.

public/llms.txt

@@ -31,7 +31,7 @@ Dogs, cats, birds, horses, rabbits, guinea pigs, hamsters, mice, rats, chinchill
 
 ## Getting started
 
-- [Sign up](https://pawfeed.org/sign-up): Create an owner account, then create a profile for a pet — an owner account can manage several pets. New sign-ups may currently require an invite.
+- [Sign up](https://pawfeed.org/sign-up): Create an owner account, then create a profile for a pet — an owner account can manage several pets. Open to everyone, no invite needed.
 - [Log in](https://pawfeed.org/log-in): Existing members sign back in here.
 
 ## Policies