[Functions] Expand the readme.md file and add two new VNET scripts

[ggailey777]

Description

• Expand the readme.md file with instructions on how to configure and run the scripts.
• Add two new VNET-based scripts:
  • Function app with storage secured by VNET.
  • Function app itself secured by VNET.

Checklist

• Scripts in this pull request are written for the bash shell.
• This pull request was tested on at least one of the following platforms:
  • Linux
  • Azure Cloud Shell
  • macOS
  • Windows Subsystem for Linux
• The most recent test date and test method are recorded in the script file.
• Scripts do not contain passwords or other secret tokens that are not randomized.
• No deprecated commands or arguments are used. (Release notes)
• All Azure resource identifiers which must be universally unique are guaranteed to be so.
• Resource names use a random function to ensure scripts can be run multiple times in quick succession without error.
• All scripts can be run in their entirely without user input.

Testing information

CLI version:

az --version

Extensions required:

[mikefrobbins]

@ggailey777, sign-off on this PR once you're ready for it to be merged.