Adds ESM usage instructions (#606)

* docs: adds ESM usage instructions

* fix: moves ESM syntax to "Dynamically" section

Author: ajmeese7

docs/usage.md

@@ -44,6 +44,17 @@ petstore.listPets().then(({ data, status, headers, res }) => {
 });
 ```
 
+Alternatively, you can use the ESM syntax:
+
+```js
+import api from 'api';
+const petstore = api('@petstore/v1.0#tl1e4kl1cl8eg8');
+
+petstore.listPets().then(({ data, status, headers, res }) => {
+  console.log(`My pets name is ${data[0].name}!`);
+});
+```
+
 The OpenAPI definition is automatically downloaded, cached, and transformed into a chainable [`fetch`](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API) Promise that you can use to make API requests.
 
 > 📘

packages/api/README.md

@@ -43,7 +43,18 @@ const petstore = require('api')(
   'https://raw.githubusercontent.com/OAI/OpenAPI-Specification/main/examples/v3.0/petstore.json'
 );
 
-petstore.listPets().then(({ data })) => {
+petstore.listPets().then(({ data }) => {
+  console.log(`My pets name is ${data[0].name}!`);
+});
+```
+
+The ESM syntax is supported as well:
+
+```js
+import api from 'api';
+const petstore = api('@petstore/v1.0#tl1e4kl1cl8eg8');
+
+petstore.listPets().then(({ data }) => {
   console.log(`My pets name is ${data[0].name}!`);
 });
 ```