docs: fix the link to the upgrade guide (#228)

# Pull Request

## Issue
https://github.com/Azure/ALZ-PowerShell-Module/issues/226

Issue #, if available:
226
## Description

Description of changes:

## License

By submitting this pull request, I confirm that my contribution is made
under the terms of the projects associated license.

Author: gcbikram

docs/wiki/Frequently-Asked-Questions.md

@@ -188,4 +188,4 @@ Alternatively, if you are also supplying a custom bootstrap module, you can spec
 [//]: # "INSERT LINK LABELS BELOW"
 [//]: # "************************"
 
-[wiki_upgrade_process]:                                              Upgrade-Process "Wiki - Upgrade Process"
+[wiki_upgrade_process]:                                              Upgrade-Guide "Wiki - Upgrade Process"