add SVG to favicon options

[Rudxain]

Fixes #486

• [x] Check the commit's or even all commits' message styles matches our requested structure.
• [x] Check your code additions will fail neither code linting checks nor unit test.

Short description of what this resolves:

Adds SVG favicon as another recommended alternative in the README.md, warning not to use it when targeting old browsers

Proposed changes:

• self-explanatory

👍 Thank you!

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Rudxain]

@thedaviddias ?

[thedaviddias]

Sorry @Rudxain I missed the notification. Let me get this merged!