Broken link in readme

### Issue Details
There is a bad link in a readme file in this project - see below.

### Repro steps (*if necessary, delete otherwise*)
1. Go to this URL: https://github.com/Azure/azure-quickstart-templates/tree/master/quickstarts/microsoft.customproviders/custom-rp-with-function
2. Click on bottom link, called [Creating an azure function](https://github.com/Azure/azure-quickstart-templates/blob/master/quickstarts/microsoft.customproviders/custom-rp-with-function/SampleFunctions/CSharpSimpleProvider/README.md)

That gives you a 404 error. I assume the content has been moved.

Open the README in quickstarts/microsoft.customproviders/custom-rp-with-function and inspect its bottom "Creating an azure function" link. Find the current location of the referenced README, update the broken link, and verify that it resolves without a 404.

Written by the indexing model from the issue text.