Add minor updates/fixes to readme

[diksipav]

Context

Updated the README.md.

What

• remove langchain installation (the example works without it),
• updated the server start command to ./indexify-server --dev (it was using -dev instead of --dev),
• removed unused Union import from typing, and collection variable.

Additionally, since the server binary is unsigned, macOS flags it as quarantined and prevents it from running. To work around this I used the xattr command to remove the quarantined flag.

And maybe in the section when running the server and executors locally after:

from tensorlake import RemoteGraph
remote_graph = RemoteGraph.by_name("text_embedder")

the invocation can be added:

invocation_id = graph.run(input={"text": "This is a test text"}, block_until_done=True)
print(f"Invocation ID: {invocation_id}")
embedding = graph.output(invocation_id, "embedder")
print("Embedding: ", embedding)

because it runs asynchronously and block_until_done=True is needed in order to wait for the response.