Add the bash command to `pip install` the package directly in the README
for a quicker start.
Also add “SDK” after “Toolbox LangChain” to clearly show that “Toolbox
LangChain” is an SDK.
> [!NOTE]
> We had released the PyPI package for Toolbox LangChain SDK as
`toolbox-langchain` and not `toolbox-langchain-sdk` but it still makes
sense to call it “Toolbox LangChain SDK” in natural language.
This is a continuation of #218, which add a local quickstart for running
Toolbox with Python and LangGraph.
---------
Co-authored-by: Twisha Bansal <twishabansal@google.com>
Co-authored-by: Anubhav Dhawan <anubhav756@gmail.com>
