Fix incorrect links and whitespace in docs

[shirohana]

I found a typo in the doc, it caused the docs site generates an invalid link.

I fixed that and also take a look in docs, and modify some indents and newlines for keeping the doc looks consistently (๑ơ ω ơ)

docs/about-handlers.md

  ...
  Gesture handler library exposes a set of components normally available in React Native that 
- are wrapped in [`NativeViewGestureHandler`](handler-native.md).
+ are wrapped in [`NativeViewGestureHandler`](handlers.md).

[jakub-gonet]

Thanks for your contribution! 🎉

I'm not sure if native-handler.md should be changed to handlers.md, but I think we can redirect it there for now.