Write interactive examples for pkg.go.dev

[ravsii]

There are examples in README.md and examples folder. (They're basically a copy of each other)

It would be great to add them directly to pkg.go.dev docs for interactive execution, like in some standard packages.

1. Example 1: regexp package https://pkg.go.dev/regexp#example-Regexp.FindString
2. Example 2: reflect package https://pkg.go.dev/reflect#example-TypeOf