add feature branch deployment example

Author: MattCordell

README.md

@@ -6,6 +6,7 @@
 
 - **Production (Stable)**: [https://mattcordell.github.io/Stoker/](https://mattcordell.github.io/Stoker/)
 - **Development (Latest Features)**: [https://stoker-dev.netlify.app/](https://stoker-dev.netlify.app/)
+- **Feature Branches**: `https://[branch-name]--stoker-dev.netlify.app/`
 
 ## Purpose