[2.2] Bootstrap PropertyAccess component documentation

[wouterj]

This component is created recently, it should be added to the 2.2 documentation. More information can be found in the subtree: https://github.com/symfony/PropertyAccess

Recommended sections:

• Introduction
• Installation
• Usage

@weaverryan this should get a 'Actionable' and 'Components' label and the milestone should be 2.2