Add yarn in the Prerequisites section of frontend document file local.md

[Bhadresh Savani]

While setting up badgeyay frontend locally user needs to have the yarn as a package manager because it's used in our project. We have to use yarn install command while setting up frontend locally.

This Prerequisite is not mentioned in the file

If the user doesn't have yarn installed, the user will get the following error
'yarn' is not recognized as an internal or external command, operable program or batch file.

to resolve this user need to hit npm install -g yarn command in command prompt

We need to add this thing in file