Add link to example repos (new and old versions)

[evangrim]

Feature Request

E.g. for https://react-native-community.github.io/upgrade-helper/?from=0.62.2&to=0.63.4, add a link to a playground or repo where 0.62.2 can be examined, and another for 0.63.4

Why it is needed

Because some packages require "custom installation steps", and those packages can become blockers to upgrading; it'd be helpful to have easy access to what a full working example should look like.

Possible implementation

Code sample