add missing key warning to README (#2238)

README.md

@@ -61,6 +61,39 @@ const customer = await stripe.customers.create({
 console.log(customer.id);
 ```
 
+> [!WARNING]
+> If you're using `v17.x.x` or later and getting an error about a missing API key despite being sure it's available, it's likely you're importing the file that instantiates `Stripe` while the key isn't present (for instance, during a build step).
+> If that's the case, consider instantiating the client lazily:
+>
+> ```ts
+> import Stripe from 'stripe';
+>
+> let _stripe: Stripe | null = null;
+> const getStripe = (): Stripe => {
+>   if (!_stripe) {
+>     _stripe = new Stripe(process.env.STRIPE_SECRET_KEY as string, {
+>       // ...
+>     });
+>   }
+>   return _stripe;
+> };
+>
+> const getCustomers = () => getStripe().customers.list();
+> ```
+>
+> Alternatively, you can provide a placeholder for the real key (which will be enough to get the code through a build step):
+>
+> ```ts
+> import Stripe from 'stripe';
+>
+> export const stripe = new Stripe(
+>   process.env.STRIPE_SECRET_KEY || 'api_key_placeholder',
+>   {
+>     // ...
+>   }
+> );
+> ```
+
 ### Usage with TypeScript
 
 As of 8.0.1, Stripe maintains types for the latest [API version][api-versions].
@@ -197,7 +230,7 @@ const stripe = Stripe('sk_test_...', {
 | `host`              | `'api.stripe.com'` | Host that requests are made to.                                                                                                                                                                                                                   |
 | `port`              | 443                | Port that requests are made to.                                                                                                                                                                                                                   |
 | `protocol`          | `'https'`          | `'https'` or `'http'`. `http` is never appropriate for sending requests to Stripe servers, and we strongly discourage `http`, even in local testing scenarios, as this can result in your credentials being transmitted over an insecure channel. |
-| `telemetry`         | `true`             | Allow Stripe to send [telemetry](#telemetry).                                                                                                                                                                             |
+| `telemetry`         | `true`             | Allow Stripe to send [telemetry](#telemetry).                                                                                                                                                                                                     |
 
 > **Note**
 > Both `maxNetworkRetries` and `timeout` can be overridden on a per-request basis.
@@ -543,14 +576,13 @@ const stripe = new Stripe('sk_test_...');
 const response = await stripe.rawRequest(
   'POST',
   '/v1/beta_endpoint',
-  { param: 123 },
-  { apiVersion: '2022-11-15; feature_beta=v3' }
+  {param: 123},
+  {apiVersion: '2022-11-15; feature_beta=v3'}
 );
 
 // handle response
 ```
 
-
 ## Support
 
 New features and bug fixes are released on the latest major version of the `stripe` package. If you are on an older major version, we recommend that you upgrade to the latest in order to use the new features and bug fixes including those for security vulnerabilities. Older major versions of the package will continue to be available for use, but will not be receiving any updates.