docs(ionic): add guide for setting up with ionic

[mhartington]

Checklist

• Issue number for this PR: #nnn (required)
  Specific docs for Ionic and Ionic CLI #1003
• Docs included?: (yes/no; required for all API/functional changes)
  Yes
• Test units included?: (yes/no; required)
  No, N/A
• e2e tests included?: (yes/no; required for multi-function/multi-class changes)
  No, N/A
• In a clean directory, npm install, npm run build, and npm test run successfully? (yes/no; required)
  Yes

Description

Fix for #1003. Added section an link to a specific Ionic/Ionic CLI installation and setup.

Code sample

N/A

[markgoho]

Can you change the Firebase config to use the environment.ts file that is demonstrated in the initial setup? We need to be consistent about how folks should be adding their config information.

[mhartington]

Ionic's CLI does not generate a environment.ts by default, so users would have to make that themselves. I can add that though.

[thorizer]

@mhartington thanks a lot for the updated docs ! there is something missing thought .
What if I want to implement firebase as a provider not just inside home.ts .