Fix Example

[bf]

Example code was not runnable due to lack of dependencies.

• Added includes
• Wrapped into fn main() { } to ensure it can be copy-pasted

Fixes #6

[djugei]

Hey, thanks for the PR, but the readme is auto-generated from lib.rs (which includes the includes etc)
therefore if this is to be merged it needs to be changed in lib.rs and done in a way that is compatible with both places, specifically it needs to allow rustdoc/doctests to run.