Document possible usage of ExternalDNS

[jonatasbaldin]

Since #7 was merged, we can use ExternalDNS to automatically create DNS entries for the FunctionIngress.

We could document this behaviour, including:

• How to setup ExternalDNS and linking to their documentation
• How to verify that the DNS was created

What do you think? Any more ideas on what do document?

[jonatasbaldin]

Here's an example on how this works: https://gist.github.com/jonatasbaldin/17379c34d5cc20815933edaeb42311fa

[alexellis]

Did it work? I can't access it from here

[alexellis]

Documenting the annotations would be useful.

[jonatasbaldin]

It did work, I just removed after my testing heh

By default there are no annotations, it depends on the ExternalDNS configuration. It could manage DNS for Ingresses, Services etc.

We could document how it to use it with the default ExternalDNS and point to their documentations if the user wants to have something more specific. What do you think?