Update Finance and Purchasing Workflow and Update help guide documentation

[dianamartin]

Need to update documentation for the enhancement:

• [x] Update Finance and Purchasing Workflow
• [x] Help guide on new change
• [x] Document what happens when they "Return to Requester"
• [x] Document what happens when they "Cancel"
• [x] Document what happens when they try to "Withdraw"

[dianamartin]

Created help guide about what happens when something is in a particular status. https://github.com/cityofaustin/atd-finance-purchasing/wiki/What-Happens-When...