chore: set up basic package config and readme

packages/signal-polyfill/package.json

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+{
+  "name": "signal-polyfill",
+  "version": "0.1.0",
+  "description": "A polyfill for the TC39 Signals proposal.",
+  "main": "dist/index.js",
+  "type": "module",
+  "types": "dist/index.d.ts",
+  "scripts": {
+    "build": "tsc -b tsconfig.json",
+    "watch": "tsc -b tsconfig.json -watch"
+  },
+  "author": "EisenbergEffect",
+  "license": "MIT"
+}

packages/signal-polyfill/readme.md

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+# Signal Polyfill
+
+A "signal" is a proposed first-class JavaScript data type that enables one-way data flow through cells of state or computations derived from other data.
+
+This is a polyfill for the `Signal` API that makes these capabilities available in browsers that don't yet support them natively.
+
+# Examples
+
+## Using signals
+
+```js
+import { Signal } from "signal-polyfill";
+import { effect } from "./effect.js";
+
+const counter = new Signal.State(0);
+const isEven = new Signal.Computed(() => (counter.get() & 1) == 0);
+const parity = new Signal.Computed(() => isEven.get() ? "even" : "odd");
+
+effect(() => console.log(parity.get()));
+
+setInterval(() => counter.set(counter.get() + 1), 1000);
+```
+
+> [!NOTE]
+> The signal proposal does not include an `effect` API, since such APIs are often deeply integrated with rendering and batch strategies that are highly framework/library dependent. However, the proposal does seek to define a set of primitives that library authors can use to implement their own effects.
+
+### Creating a simple effect
+
+```js
+import { Signal } from "signal-polyfill";
+
+let needsEnqueue = false;
+
+const w = new Signal.subtle.Watcher(() => {
+  if (needsEnqueue) {
+    needsEnqueue = false;
+    queueMicrotask.enqueue(processPending);
+  }
+});
+
+function processPending() {
+  needsEnqueue = true;
+
+  for (const s of w.getPending()) {
+    s.get();
+  }
+
+  w.watch();
+}
+
+export function effect(callback) {
+  let onUnwatch;
+  const computed = new Signal.Computed(() => onUnwatch = callback(), {
+    [Signal.subtle.unwatched]() {
+      typeof onUnwatch === "function" && onUnwatch();
+    }
+  });
+
+  w.watch(computed);
+  computed.get();
+
+  return () => w.unwatch(computed);
+}
+```
+
+> [!IMPORTANT]
+> The `Signal.subtle` APIs are so named in order to communicate that their correct use requires careful attention to detail. These APIs are not targeted at application-level code, but rather at framework/library authors.