Add more examples for remote env value files

[reixd]

I had difficulties loading remote value files even after looking at the docs here and go-getter.
The solution was in the test code here:

helmfile/pkg/remote/remote_test.go

Line 67 in ae942c5

// We use `@` to separate dir and the file path. This is a good idea borrowed from helm-git:

Use an @ to separate the path from the GIT url...

To help others I want to update the docs with the solution which worked for me ;-)

[mumoshu]

I'm now wondering if this was never correct 🤔 Perhaps it should be git::https://git.company.org/helmfiles@global/us-west.yaml?ref=master ?

[reixd]

Yes, you need to use the @ to separate the folder from the URL.

[mumoshu]

Ah, good catch! I do often forget about the fact that we need to use @ myself, so this's a great addition. Thanks for your contribution @reixd