Fix IHR_API_BASE local url in README.md

[xSkkarf]

Description:

The docs for working with a local instance of IHR website suggest that the IHR_API_BASE should be set to http://127.0.0.1:8000/, which lacks the /ihr/api/ part.

Current url:

http://127.0.0.1:8000/

Correct url:

http://127.0.0.1:8000/ihr/api/

Notes:

It is a minor issue, but it took me sometime till I figured out what was wrong.