README.md added to rustecal-core (#22)

Author: rex-schilasky

rustecal-core/README.md

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+# rustecal-core
+
+**Idiomatic Rust API for Eclipse eCAL**
+
+`rustecal-core` provides high-level Rust abstractions for eCAL’s pub/sub and service/client patterns, built on top of the low-level FFI bindings in [`rustecal-sys`](https://crates.io/crates/rustecal-sys).
+
+---
+
+## Features
+
+- **Core Initialization & Lifecycle**: Initialize, finalize, retrieve version information, component selection via `EcalComponents` bitflags.
+- **Configuration**: Flexible configuration via environment variables and builder patterns.
+- **Monitoring**: Inspect the eCAL runtime state including process, topic, and service/client details.
+- **Logging**: Emit and retrieve log messages at various severity levels.
+- **Error Handling**: Comprehensive `RustecalError` enum for FFI errors and internal issues.
+
+## Requirements
+
+- **Rust** 1.60 or later  
+- **eCAL** C/C++ library v6.0 or later installed and accessible on your system
+- **rustecal-sys** v0.1.0 or later  
+
+## Installation
+
+Add `rustecal-core` to your `Cargo.toml`:
+
+```toml
+[dependencies]
+rustecal-core = "0.1.0"
+```