Update index.rst

[miguelcrpinto]

Improved the description of the AddEnvironmentVariables prefix parameter.

The prefix is being removed from the environment variable names and it was not mentioned anywhere. You had to guess...

[dnfclas]

Hi @miguelcrpinto, I'm your friendly neighborhood .NET Foundation Pull Request Bot (You can call me DNFBOT). Thanks for your contribution!

This seems like a small (but important) contribution, so no Contribution License Agreement is required at this point. Real humans will now evaluate your PR.

TTYL, DNFBOT;

[Rick-Anderson]

@divega does this need clarification?

[divega]

@Rick-Anderson I think the change looks good (although it is missing a period at the end). The prefix is used as a filter (which was already captured in the first sentence) but it is also removed from the environment variable names to create the configuration keys.

[Rick-Anderson]

@danroth27 @spboyer how do we want to handle this?

[spboyer]

Since this is a /// comment should the PR go against the aspnet code here:

https://github.com/aspnet/Configuration/blob/47b13050126fab7afa18e8636bb3c5d1f4022338/src/Microsoft.Extensions.Configuration.EnvironmentVariables/EnvironmentVariablesExtensions.cs#L29

[miguelcrpinto]

I felt that this needed some clarification because the parameteless overload of the method just loads all environment variables and doesn't modify their name.

I do agree with the suggestion from @spboyer , this behavior should be mentioned both in the documentation (with something like what I proposed) and in the /// comments.

I spent almost 2 hours trying to figure out what was going wrong with my environment variables until I decided to dive into the method source.

[Rick-Anderson]

@miguelcrpinto can you open an issue at https://github.com/aspnet/Configuration/blob/47b13050126fab7afa18e8636bb3c5d1f4022338/src/Microsoft.Extensions.Configuration.EnvironmentVariables/EnvironmentVariablesExtensions.cs#L29

[miguelcrpinto]

Done: aspnet/Configuration#488