This is the initial go at the library.

This is the initial pass. It sets some things up and lets me get
some ideas out of my head.

README.md

@@ -1,3 +1,51 @@
 # ccsds_spp
 
-CCSDS Space Packet Protocol
+A `no_std`, heapless Rust implementation of the
+[CCSDS Space Packet Protocol][SPP], suitable for embedded and real-time
+systems.
+
+This library is intended for use in satellite software, space simulation,
+and telemetry/telecommand tooling. It is designed to be robust, portable,
+and usable in constrained environments. No allocator required.
+
+---
+
+## Features
+
+* `no_std` compatible
+* Heapless: works in memory-constrained environments
+* Bit-accurate parsing and encoding
+* `FromBits` / `IntoBits` traits for masked operations
+* CCSDS-compliant `Version`, `PacketType`, `APID` support
+* Designed for integration into embedded systems or FFI-safe libraries
+
+---
+
+
+## Example
+
+```rust
+use ccsds_space_packet::{PacketHeader, PacketType, Version, ApId};
+
+let mut header = PacketHeader { data: [0u8; 6] };
+
+header.set_version(Version::One);
+header.set_packet_type(PacketType::Telemetry);
+header.set_ap_id(ApId::from(42));
+
+assert_eq!(header.get_version(), Version::One);
+assert_eq!(header.get_packet_type(), PacketType::Telemetry);
+assert_eq!(u16::from(header.get_ap_id()), 42);
+```
+
+## Design Notes
+
+This is a work in progress.
+
+Focus is on correctness and portability over performance for now.
+
+Library avoids panics where possible and returns Result<T, &str> for error handling.
+
+
+## References
+[SPP]: https://ccsds.org/wp-content/uploads/gravity_forms/5-448e85c647331d9cbaf66c096458bdd5/2025/01//133x0b2e2.pdf "CCSDS Space Packet Protocol PDF"