Fix links in SDK documentation

[andreas-aman]

When reading the documentation https://github.com/DopplerHQ/node-sdk/blob/main/src/services/README.md it seems the linking is broken.

If I click on Secrets and then on Get I'm expecting to be sent to the details about using Get for Secrets. But instead I get sent to the first occurrence of the Get title.

This means I need to manually scroll through the documentation to find what I'm looking for. Quite the annoyance.