SQSCANGHA-54 Improve the README

[antonioaversa]

Follow-up to #152 with minor adjustments to the README.

[henryju]

Please don't mention the Java keystore, as this is implementation details.

Also, I know the env variable is named ROOT_CERT, but this is misleading. It doesn't have to be a root certificate. It can be the server certificate or any other intermediate CA certificate.

[antonioaversa]

Please don't mention the Java keystore, as this is implementation details.

Also, I know the env variable is named ROOT_CERT, but this is misleading. It doesn't have to be a root certificate. It can be the server certificate or any other intermediate CA certificate.

Understood. I have removed it from the description of the env var above. I couldn't find mentions of root certificate or Java keystore anywhere else in the repo, so we should be good now.