Add a GPL v3 LICENSE file (#22)

* Add a LICENSE file

* added license, thanks @bnb

* script to print licenses

* Change to GPL v3

I believe it is necessary because of fnm's dependencies. If it's not, I'd be happy to make it more open

* Update package.json

.ci/print-licenses.js

@@ -0,0 +1,43 @@
+#!/usr/bin/env node
+
+const { execSync } = require("child_process");
+
+const groupByMap = (xs, fn, mapFn) => {
+  const grouped = {};
+
+  for (const x of xs) {
+    const key = fn(x);
+    grouped[key] = grouped[key] || [];
+    grouped[key].push(mapFn(x));
+  }
+
+  return grouped;
+};
+
+const licenses = execSync('grep -r "license:" esy.lock')
+  .toString()
+  .split("\n")
+  .map(x => x.trim())
+  .filter(Boolean)
+  .map(line => {
+    const [path, , license] = line.split(":");
+    const dependency = path
+      .split("/")
+      .slice(1)
+      .join("/")
+      .match(/^(.+)\/[^/]+$/)[1];
+    return { dependency, license: JSON.parse(license.trim()) };
+  });
+
+const byLicense = groupByMap(
+  licenses,
+  ({ license }) => license,
+  ({ dependency }) => dependency
+);
+
+for (const [license, packages] of Object.entries(byLicense)) {
+  console.log(`${license}:`);
+  for (const package of packages) {
+    console.log(`  - ${package}`);
+  }
+}