docs: add Hindsight long-term memory integration to README

[benfrank241]

Summary

I'd like to add a community integrations section to the README introducing hindsight-strands, a third-party package that gives Strands agents persistent long-term memory via Hindsight.

What it looks like

The tools are standard @tool functions that plug directly into Agent(tools=[...]):

from strands import Agent
from hindsight_strands import create_hindsight_tools

tools = create_hindsight_tools(
    bank_id="user-123",
    hindsight_api_url="http://localhost:8888",
)

agent = Agent(tools=tools)
agent("Remember that I prefer dark mode")
agent("What are my preferences?")

The agent gets three tools: hindsight_retain (store), hindsight_recall (search), and hindsight_reflect (synthesize). Full docs at hindsight.vectorize.io/docs/sdks/integrations/strands.

Proposed change

Add a ## Community Integrations section to the README between the "Bidirectional Streaming" subsection and ## Documentation. Happy to submit a PR if this is welcome.