Add README

Add a readme file.

Signed-off-by: Pieter De Gendt <[email protected]>

README.md

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+# COBS
+
+A Golang module for the
+[Consistent Overhead Byte Stuffing (COBS)](https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing)
+algorithm. 
+
+## Usage
+
+This module provides both simple helper functions to Encode/Decode `[]byte` arrays and 
+Encoder/Decoder structs to stream bytes to an `io.Writer` instance.
+
+### `Encode`/`Decode` functions
+
+The helper functions will allocate buffers to hold the encoded/decoded data and return a `[]byte`
+slice or an error.
+
+The following example encodes a string with embedded zeroes:
+
+```go
+package main
+
+import (
+	"os"
+
+	"github.com/pdgendt/cobs"
+)
+
+func main() {
+	enc, _ := cobs.Encode([]byte{'H', 'e', 'l', 'l', 'o', 0x00, 'w', 'o', 'r', 'l', 'd', '!'})
+
+	os.Stdout.write(enc)
+}
+```
+
+### `Encoder`/`Decoder` structs
+
+The structs require an `io.Writer` instance on creation. As soon as data is available it is written,
+for the `Encoder` this is done for each group, with a maximum of 255 bytes, for the `Decoder` every
+`byte` is written individually.
+
+The structs implement the `io.Writer` interface to allow chaining.
+
+The following example encodes bytes read from `os.Stdin` and writes them to `os.Stdout`:
+
+```go
+package main
+
+import (
+	"io"
+	"os"
+
+	"github.com/pdgendt/cobs"
+)
+
+func main() {
+	enc := cobs.NewEncoder(os.Stdout)
+
+	if _, err := io.Copy(enc, os.Stdin); err != nil {
+		panic(err)
+	}
+
+	// Close needs to be called to flush the last group
+	if err := enc.Close(); err != nil {
+		panic(err)
+	}
+}
+```
+
+## CLI tools
+
+The [cmd/](cmd/) directory contains simple encode/decode command line tools that take in data
+from `stdin` and writes it to `stdout`.
+
+This can be used to pipe encoded/decoded data to other processes.
+
+```shell
+$ echo "Hello world" | go run cmd/encode/main.go | go run cmd/decode/main.go
+Hello world
+```