Updated usage example in README

[masza]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[X] Other... Please describe: README update

What is the current behavior?

Current usage example thrown error:
ConfigurationError: Invalid protocol: 'localhost:'

Issue Number: N/A

What is the new behavior?

No error during module registration.

Does this PR introduce a breaking change?

[ ] Yes
[X] No