feat(README): private-key-converter web ui(#94)

* add private-key-converter to README.md

* Update README.md

Author: babblebey

README.md

@@ -191,6 +191,12 @@ You can identify the format based on the the first line
 
 ### Converting `PKCS#1` to `PKCS#8`
 
+- #### Using an Online Private Key Converter
+
+Convert quickly using the Web interface at https://private-key-converter.vercel.app
+
+- #### Using Node.js
+
 If you use Node.js, you can convert the format before passing it to `universal-github-app-jwt`:
 
 ```js
@@ -210,7 +216,9 @@ const { token, appId, expiration } = await githubAppJwt({
 });
 ```
 
-But we recommend to convert the format using `openssl` before passing it to your app.
+- #### Using OpenSSL
+
+Convert the format using `openssl` before passing it to your app.
 
 ```
 openssl pkcs8 -topk8 -inform PEM -outform PEM -nocrypt -in private-key.pem -out private-key-pkcs8.key