docs: add detailed information to FASTElement on template bindings

[janechu]

🙋 Documentation Request

We currently do not have a document that explains exactly the mechanisms for how bindings attach to pieces of DOM and update them. This would be extremely helpful when identifying bugs and pursuing binding related work such as hydration.

💁 Possible Solution

Create a markdown file in an appropriate location in @microsoft/fast-element describing how bindings are created and updated.

There are also various binding types, these should be enumerated and explained on each of their use cases with examples.