docs(basti): document new --bastion-assign-public-ip option

[BohdanPetryshyn]

Proposed Changes

This PR documents the new --bastion-assign-public-ip option introduced in #115.

Related Issues/PRs

103

Checklist

• [x] I cleaned up my code.
• [x] All the tests and checks passed (npm run test).
• [x] I have added necessary documentation and/or updated existing documentation.
• [x] I have added or modified tests to cover the changes.