Add react-native-svg sample

[chrisglein]

react-native-svg is one of the most popular and fundamental libraries. On Windows the module is supported on Paper, and in active development for Fabric. It's a dependency needed by some other modules like #425. But really... it should have its own sample page!

It doesn't need to do a ton. Just show a few examples of how to get an inline SVG or file/uri SVG working. Enough to show folks that its there for them for their vector graphics needs.