Add service doc for currencyservice

[lalitb]

Bug Report

Documentation for currency service is missing here - https://github.com/open-telemetry/opentelemetry-demo/tree/main/docs/services

Symptom

A clear and concise description of what the bug is.

What is the expected behavior?

Documentation should be available.

What is the actual behavior?

Documentation is missing.

Reproduce

Look for the documentation here - https://github.com/open-telemetry/opentelemetry-demo/tree/main/docs/services

We will close this issue if:

N/A

Additional Context

N/A

[lalitb]

Please assign it to me. Thanks.