Documentation for valid binding names

Add documentation to provide guidance for customers to create valid binding names and avoid errors. This documentation could be used in a forward link when there are errors at [this step](https://github.com/Azure/azure-functions-host/blob/cfa63f6c4e149363fc3792608b6c3581e3501fda/src/WebJobs.Script/Utility.cs#L590) of binding name validation.