Add Azure Sync Instructions to README

[nickevansuk]

Add the instructions below to README.md

Updating an Azure RPDE Proxy installation

1. Find the resource group in which the Azure RPDE Proxy was originally deployed

2. Select the Azure function from the list of resources (look for the lightning icon)

3. Open the 'Platform features' tab at the top

4. Click the 'Deployment Center' link

5. Click the 'Sync' button