Add repo map

DEVELOPING.md

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+# Developer Guide
+
+
+## Repository Map
+```mermaid
+flowchart TD
+
+    NIM("<a href="https://github.com/logos-messaging/nim-chat-poc"><b>nim-chat-poc</b><br>c-bingings, process control, networking</a>")
+    LIB("<a href="https://github.com/logos-messaging/libchat"><b>libchat</b><br>encryption, encoding</a>")
+    PROTO("<a href="https://github.com/logos-messaging/chat_proto"><b>chat_proto</b><br>protobufs, language specific types</a>")
+    LMN("<a href="https://github.com/logos-messaging/logos-messaging-nim"><b>logos-messaging-nim</b><br>p2p networking</a>")
+
+
+    NIM --> LIB
+    NIM --> LMN
+    LIB --> PROTO
+
+%% Mark External Dependencies
+style LMN fill:#fff 
+
+```
+
+## Repositories
+
+### nim-chat-poc
+Root of the Logos chat SDK, written in Nim.
+
+Handles async operations and bridges network operations with the cryptographic backend.
+
+**Responsibilities:**
+- C bindings to libchat
+- Async execution (Chronos)
+- Network integration
+
+### libchat
+Cryptographic logic implementation in Rust.
+
+Operates as a pipeline: accepts either encrypted payloads or plaintext content, returns the other. Encrypted payloads can be sent directly to network clients; decrypted content goes to applications.
+
+**Responsibilities:**
+- Cryptographic implementations
+- Encoding/decoding
+
+
+### logos-messaging-nim
+P2P networking layer using logos-messaging protocol.
+
+Provides decentralized message transport. This is an external dependency.
+
+### chat_proto
+Protobuf definitions.
+
+Defines the protobufs used in the logos-chat protocol and provides generated types for various languages.