Add readme

README.md

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+# `permchain`
+
+## Get started
+
+`pip install permchain`
+
+## Usage
+
+```python
+from permchain import InMemoryPubSubConnection, PubSub, Topic
+
+topic_one = Topic("one")
+chain_one = Topic.IN.subscribe() | (lambda x: x + 'b') | topic_one.publish()
+chain_two = topic_one.subscribe() | (lambda x: x + 'c') | Topic.OUT.publish()
+
+conn = InMemoryPubSubConnection()
+pubsub = PubSub(processes=(chain_one, chain_two), connection=conn)
+
+assert pubsub.invoke('a') == ['abc']
+```
+
+Check `tests` and `examples` for more examples.
+
+## Roadmap
+
+- [ ] Add initial retry support (pending changes in `langchain`)
+- [ ] Detect cycles (aka. infinite loops) and throw an error
+  - [ ] Allow user to catch that error (by subcribing to an error topic?)
+- [ ] Replace Queue data structure with a Log data structure (this will enable checking the status of the readers, etc.)
+  - [ ] eg. https://anyio.readthedocs.io/en/3.x/streams.html
+  - [ ] Implement IN and OUT topics as regular topics
+- [ ] Enable resuming PubSub from the "middle" of the computation
+- [ ] Add Redis-backed Connection implementation

permchain/__init__.py

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+from permchain.pubsub import PubSub
+from permchain.topic import Topic
+from permchain.connection_inmemory import InMemoryPubSubConnection
+
+__all__ = [
+    "PubSub",
+    "Topic",
+    "InMemoryPubSubConnection",
+]