basic 'hello world' repo has been archived

[jekennedy]

Overview The basic 'hello world' repo has been archived, so this PR removes the dead link.

Considerations We could consider adding this 'hello world' sample instead, but it's not part of this 'examples' repo.

[marc0olo]

I think we now advertise this one here:

• https://github.com/dfinity/icp-hello-world-motoko

but as this is outside the repo it shouldn't be referenced in the README here 👍