Added link to signup from sign-in page

[skwowet]

Changes proposed ✍️

Added "Don't have an account yet? Create an account" copy to the bottom of the sign-in form on app.crowd.dev/auth/signin

Reference issue: #766

• Screenshots

Checklist ✅

• Label appropriately with Feature, Enhancement, or Bug.
• Tests are passing.
• New backend functionality has been unit-tested.
• Environment variables have been updated:
  • Local frontend configuration: frontend/.env.dist.local, frontend/.env.dist.composed.
  • Local backend: backend/.env.dist.local, backend/.env.dist.composed.
  • Configuration docs have been updated.
  • Team members only: update environment variables in override, staging and production env. files and trigger update config script.
• API documentation has been updated (if necessary) (see docs on API documentation).
• Quality standards are met.
• All changes have been tested in a staging site.
• All changes are working locally running crowd.dev's Docker local environment.

[skwowet]

Should the checklist items be marked by the contributor?

[CLAassistant]

All committers have signed the CLA.

[jonathimer]

Awesome, thanks for this contribution! 🤩

[skwowet]

@jonathimer You're welcome <3

[jonathimer]

added you to our brand-new community contributors wall 🥂