Improved Documentation re ENIConfig Environment Variables

[taylorb-syd]

Issue #, if available: N/A

Description of changes:

• Reviewed the ENIConfig specific Environment Variable Documentation in Readme and rewrote for clarity regarding usage.
• Changed "more information" link to point to AWS Documentation rather that now out of date Pull Request Add a configuration knob to allow Pod to use different VPC SecurityGroups and Subnet #165

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mogren]

Thanks for improving the docs!

FYI, escaping parentheses and periods are only needed if they might trigger a link or ordered list. (See Markdown syntax)

Could you remove the unnecessary \s?

[taylorb-syd]

Fixed the spaces and removed a few of the redundant \s as requested. However, as we seem to be using \. almost everywhere, I have kept quite a few of of the slashes to be consistent with current formatting.