Format README.md
Format README.md

Mocha test instructions
rasata/MailDev,strategicdata/MailDev,sendwithus/tool-maildev,strategicdata/MailDev,xavierpriour/MailDev,AlexDpy/MailDev,strategicdata/MailDev,rasata/MailDev,AlexDpy/MailDev,xavierpriour/MailDev,sendwithus/tool-maildev