Create pbnj.md

Create a recipe for peanut butter and jelly sandwich
Add formatting

Add list formatting to ingredients and steps
Use numbered list for steps

Ensure steps are followed in order by giving them an order
Clarify step 2

Clarify that the peanut butter should be spread on the 2nd slice of bread in step 2.
Merge pull request #16 from CorenMajere/master

Simple lunch