Improving the example for loading the public/private keys

Description

I am trying to follow the example in README.md:

//HMAC
Algorithm algorithmHS = Algorithm.HMAC256("secret");

//RSA
RSAPublicKey publicKey = //Get the key instance
RSAPrivateKey privateKey = //Get the key instance
Algorithm algorithmRS = Algorithm.RSA256(publicKey, privateKey);

However getting the key instances is not that simple. After a lot of digging I managed to load at least the private key as follows:

I followed https://stackoverflow.com/questions/44474516/how-to-create-public-and-private-key-with-openssl to generate public and private key.
I converted private key to the DER form openssl pkcs8 -topk8 -inform PEM -outform DER -in private_key.pem -out pkcs8.der -nocrypt
Now I am able to load the private key as:

val privateKey = readKeyAsBytes("pkcs8.der")
        .run { PKCS8EncodedKeySpec(this) }
        .run { KeyFactory.getInstance("RSA").generatePrivate(this) }
        as RSAPrivateKey

However this doesn't work for generating the public key:

val publicKey = readKeyAsBytes("publickey.crt")
        .run { X509EncodedKeySpec(this) }
        .run { KeyFactory.getInstance("RSA").generatePublic(this) }
        as RSAPublicKey

as it fails with InvalidKeyException: invalid key format. I am not sure whether .getInstnace(RSA) is correct here, but I couldn't make it work with anything else either. I guess the public key is not in the X509 format, but I cannot seem to manage to convert it to it.

It would be great to provide some better example to start with this.

Prerequisites

(note this is not a bug)

[x] I have checked the documentation for this library in the README.
[x] I have checked the Auth0 Community for related posts.
[x] I have checked for related or duplicate Issues and PRs.
[x] I have read the Auth0 general contribution guidelines.
[x] I have read the Auth0 Code of Conduct.
[x] I am reporting this to the correct repository (note this library is used by many libraries, such as auth0-java).

Environment

Please provide the following:

Version of this library used: 3.9.0
Version of Java framework used: Java 11
Additional libraries that might be affecting your instance: -

Reproduction

(not a bug)

auth0 / java-jwt