chore: add documentation for running against a development service (#11)

also add an example `.env.local` file as `.env.tpl`

.env.tpl

@@ -1,2 +1,6 @@
 NEXT_PUBLIC_STRIPE_PRICING_TABLE_ID=prctbl_1NzhdvF6A5ufQX5vKNZuRhie
-NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=pk_test_51LO87hF6A5ufQX5viNsPTbuErzfavdrEFoBuaJJPfoIhzQXdOUdefwL70YewaXA32ZrSRbK4U4fqebC7SVtyeNcz00qmgNgueC
+NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=pk_test_51LO87hF6A5ufQX5viNsPTbuErzfavdrEFoBuaJJPfoIhzQXdOUdefwL70YewaXA32ZrSRbK4U4fqebC7SVtyeNcz00qmgNgueC
+
+# set these to your upload API service URL and the DID your service is using as its service DID
+NEXT_PUBLIC_W3UP_SERVICE_URL=https://up.web3.storage
+NEXT_PUBLIC_W3UP_SERVICE_DID=did:web:web3.storage

README.md

@@ -18,4 +18,18 @@ Open [http://localhost:3000](http://localhost:3000) with your browser to see the
 
 You can start editing the page by modifying `app/page.tsx`. The page auto-updates as you edit the file.
 
+### Using an alternate w3up service
+
+By default, this app connects to https://up.web3.storage. To use an alternate service, specify
+the service URL and DID in your environment variables, like:
+
+```
+NEXT_PUBLIC_W3UP_SERVICE_URL=https://your.w3up.service
+NEXT_PUBLIC_W3UP_SERVICE_DID=did:your-service-did
+```
+
+An example `.env.local` file can be found in `.env.tpl`.
+
+If you are using `w3infra`, the service URL will be displayed as the `UploadApiStack`'s `ApiEndpoint` output once `npm start` has successfully set up your development environment.
+
 <p style="text-align:center;padding-top:2rem">⁂</p>