Mention env vars in the provider config docs

[jackmtpt]

No description provided.

[sonatype-community-cla-app]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[jackmtpt]

Signing a CLA requires tedious sign-off from our legal team that I've not got time to bother with, so I guess this won't be merged.

[madpah]

Thanks for the feedback @jackmtpt.

The intent of the CLA is not to discourage contributions, although we appreciate there can be challenge with this.

If possible, we'd be keen to understand more about your situation - if you're able to share your real name and Company Name (you can drop this to community-group@sonatype.com) - we'd like to explore options to avoid the CLA where existing agreements exist between Sonatype and your company.

Thanks in advance!

[madpah]

Resolved by #29.