docs: add basic readme

README.md

@@ -1,2 +1,36 @@
-# npm
+# @semrel-extra/npm
 Drop-in-repl npm plugin to handle `npm-whoami` throttling issue for monorepos: https://github.com/semantic-release/npm/issues/414
+
+### Install
+```shell
+npm i -D @semrel-extra/npm
+```
+
+### Usage
+`@semrel-extra/npm` is just a wrapper, so it inherits the API contract of [@semantic-release/npm](https://github.com/semantic-release/npm).
+Follow [its docs](https://github.com/semantic-release/npm/blob/master/README.md):
+
+| Step               | Description |
+|--------------------|-------------|
+| `verifyConditions` | Verify the presence of the `NPM_TOKEN` environment variable, or an `.npmrc` file, and verify the authentication method is valid. |
+| `prepare`          | Update the `package.json` version and [create](https://docs.npmjs.com/cli/pack) the npm package tarball. |
+| `addChannel`       | [Add a release to a dist-tag](https://docs.npmjs.com/cli/dist-tag). |
+| `publish`          | [Publish the npm package](https://docs.npmjs.com/cli/publish) to the registry. |
+
+```json
+{
+  "plugins": [
+    "@semantic-release/commit-analyzer",
+    ["@semrel-extra/npm", {
+      ...
+    }],
+    ["@semantic-release/git", {
+      "assets": ["package.json", "npm-shrinkwrap.json"]
+    }]
+  ]
+}
+
+```
+
+### License
+[MIT](./LICENSE)