Docs: Correct directions for terminal env vars

[Nuru]

The directions for setting env vars in your terminal given in #247 are wrong.

chamber/README.md

Lines 174 to 178 in c2a0530

	To set env vars in your terminal you can eval the dotenv export format. For example,
	```shell
	eval `chamber export foo -f dotenv`
	echo $foo_var
	```

This does not work correctly with various special characters. In general, use of the dotenv format should be avoided (see #208), and especially here when we have #184 specifically to handle this use case.

Recommended change:

To set env vars in your terminal you can use the chamber env command. For example,

source <(chamber env service)`
printf "%s" "$SERVICE_VAR"

[nickatsegment]

SGTM. Wanna make a PR?

[Nuru]

@nickatsegment I'd rather not spend time on the whole fork and PR thing, if you don't mind, and I don't need attribution. Please just go ahead and fix it in your next update.