Add YAML description to each of the files under "Installing Serving Component" (development/install/any-kubernetes-cluster.md)

[omerbensaadon]

Expected Behavior

When a new users comes to the "Installing Serving Component" section of the YAML-based install page, they should be given a brief description for each of the YAML files they are applying, a link out to learn more and an understanding of what impact those YAML files will have on their cluster.

Actual Behavior

When a new users comes to the "Installing Serving Component" section of the YAML-based install page, they see 2 kubectl apply commands without much additional context.

Steps to Reproduce the Problem

1. Go to https://knative.dev/development/install/any-kubernetes-cluster/#installing-the-serving-component
2. Check out the contextual information for each of the steps
3. Be forced to investigate the YAML files in Github to understand what each of them does

Additional Info

Additional context
Child issue of knative/ux#26 part of the ongoing efforts in knative/ux#1

[omerbensaadon]

/kind good-first-issue

[snneji]

/assign

[omerbensaadon]

Closed as part of #3411