Note ENV vars In README

[bcomnes]

Add a small mention about ENV var support. Thank you!

[perrin4869]

This is only true when using postgres though. This lib also supports mssql and MySQL, and these environment variables don't work there. Maybe those clients support other environmental variables...

[bcomnes]

though this may vary with your driver.

That's what the caveat was for. Do you want me to add links to those drivers too?

[perrin4869]

Thanks!

[coveralls]

Pull Request Test Coverage Report for Build 2072719316

Warning: This coverage report may be inaccurate.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.7%) to 91.768%

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Totals
Change from base Build 2055868673:	-0.7%
Covered Lines:	467
Relevant Lines:	495

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💛 - Coveralls