Please add documentation on using multiple fetch repositories

[ProNibs]

When using multiple git repositories during the fetch stage, it's unclear how the "fetched" repositories are stored temporarily by kapp-controller.

dkalinin was super helpful in pointing out that the git repos are put into numbered repos. Be also helpful to document a more clear example as the Helm example using stable/nginx doesn't mention which Helm repo it is pulling from.

Slack discussion

[danielhelfand]

Thanks for opening this, @ProNibs. We have definitely received this feedback in the past and agree that we should document the behavior.

If you are interested in contributing this to our docs, this section might be a good location for this information. In the website code, it lives here.

We will eventually get to this, but it may not be prioritized as soon as other work. So anyone open to contributing should feel free to pick this up.

[neil-hickey]

We should still document this behaviour. Leaving open.