Document template ref typing in TS (i.e. InstanceType)

[craPkit]

To prevent issues like this, the typescript section should be amended with an exemplary declaration of a component ref's type using InstanceType.

Here's a more elaborate example: https://stackoverflow.com/questions/66907606/whats-vue-3-composition-apis-type-safe-way-of-defining-methods/66909582#66909582