docs: document default environment separator

[andyrift]

The first time I stumbled upon this I wasted like 2 hours trying to figure out how to use environment variables. It really was not obvious that a dot would be the default separator. And it is not even easy to figure out when using bash, because it refuses to accept dots!

Today I was starting a new project and it is really bothering me that this is not documented, so here is a pr with just some docs. I did not bother creating an issue, because it felt excessive.

Hopefully I did not do anything wrong and this will pr be accepted.

[coveralls]

Pull Request Test Coverage Report for Build 20149618329

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 64.052%

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Totals
Change from base Build 20146164451:	0.0%
Covered Lines:	939
Relevant Lines:	1466

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💛 - Coveralls

[epage]

Thanks!