README: Add frozen netstring example (#7)

Author: gibson042

README.md

@@ -52,6 +52,33 @@ An immutable buffer cannot be detached, resized, or further transferred. Its `ma
 
 The ArrayBuffer `slice` method and TypedArray methods that create new ArrayBuffers (`filter`, `map`, `slice`, `toReversed`, etc.) make no effort to preserve immutability, just like they make no effort to preserve resizability (although use of SpeciesConstructor in those methods means that _lack_ of resizability/immutability in the result cannot be guaranteed for the latter).
 
+## Use cases
+
+### Represent arbitrary binary data as an immutable [netstring](https://en.wikipedia.org/wiki/Netstring)
+
+```js
+// Read data from base64 input and calculate its length.
+const data = Uint8Array.fromBase64(inputBase64);
+const dataLen = data.length;
+const dataLenStr = String(dataLen);
+const digitCount = dataLenStr.length;
+
+// Transfer to a new ArrayBuffer with room for the netstring framing.
+const tmpBuf = data.buffer.transfer(digitCount + 1 + dataLen + 1);
+const tmpArr = new Uint8Array(tmpBuf);
+assert(tmpArr.buffer === tmpBuf);
+
+// Frame the data.
+tmpArr.copyWithin(digitCount + 1, 0);
+for (let i = 0; i < digitCount; i++) tmpArr[i] = dataLenStr.charCodeAt(i);
+tmpArr[digitCount] = 0x3A;
+tmpArr[tmpArr.length - 1] = 0x2C;
+
+// Transfer to an immutable ArrayBuffer backing a frozen Uint8Array.
+const netstringArr = Object.freeze(new Uint8Array(tmpBuf.transferToImmutable()));
+assert(tmpBuf.detached);
+```
+
 ## Implementations
 
 ### Polyfill/transpiler implementations