Document the send money using md files

[stephane-segning]

• User story: User story: As a PP User, I'd like to send money to another PP User using the Smartphone - Use-case v1 #19
• Description:
  • All requirements should be tested and documented
  • All errors and exceptions should be handled
• Blocker:
  • Implement the service for sending Money #20,
  • Implement the REST API for sending Money #21,
  • Implement the service for validating "sending money" #22,
  • Implement the REST API for validating "sending money" #23