add last updated date on page

[berdinatilli]

would be nice to have on https://schneegans.de/windows/unattend-generator/ page a date when it was last updated/optimized...

[cschneegans]

I have now added a link to the most recent Git commit and an approximate build timestamp:

Note that a commit does not necessarily affect the generated autounattend.xml file. For example, the latest commit only adds metadata to the .NET assembly, while a previous commit would actually change how an autounattend.xml file is generated.