Add Zig port documentation

Author: vinitkumar

ZIG_README.md

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+# Chatbot - Zig Edition
+
+This is a Zig port of the chatbot C implementation. The chatbot uses keyword matching to provide responses based on user input.
+
+## Requirements
+
+- Zig 0.15.2 or later (stable release)
+
+## Building
+
+Build the executable:
+
+```bash
+zig build-exe src/main.zig -femit-bin=zig-out/bin/chat
+```
+
+Or use the build system:
+
+```bash
+zig build
+```
+
+This will create the executable in `zig-out/bin/chat`.
+
+## Running
+
+```bash
+./zig-out/bin/chat
+```
+
+Or via the build system:
+
+```bash
+zig build run
+```
+
+## Testing
+
+Run all tests:
+
+```bash
+zig test src/chatbot.zig
+```
+
+Or via the build system:
+
+```bash
+zig build test
+```
+
+## Architecture
+
+- **chatbot.zig**: Hash table implementation for keyword-response mapping
+- **main.zig**: Interactive chatbot CLI
+
+The hash table uses chaining for collision resolution and supports inserting, updating, and retrieving key-value pairs.