Adding a key step -- to change into the packages/tinybird directory

[brooksc]

I was working through the install instructions and this step kept failing

tb push datasources

or:

tb push datasources/email.datasource

The key requirement is to cd into packages/tinybird first.

This is a minor update that adds that step to the README.

Summary by CodeRabbit

• Documentation
  • Updated the "Getting Started" section of the Tinybird package README to include a new instruction for navigating to the packages/tinybird directory after activating the virtual environment.