re-add ASPNET472CompatDoc (#668)

* re-add ASPNET472CompatDoc

* Minor edits, added links.

* Minor changes, added links.

* Changed targeted version, removed reverted section

Documentation/compatibility/aspnet-472-compat-doc.md

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+## "dataAnnotations:dataTypeAttribute:disableRegEx" app setting is on by default in .NET Framework 4.7.2
+
+### Scope
+Minor 
+
+### Version Introduced
+4.6.2
+
+### Change Description
+In .NET Framework 4.6.1, an app setting (`"dataAnnotations:dataTypeAttribute:disableRegEx"`) was introduced that allows users to disable the use of regular expressions in data type attributes (such as <xref:System.ComponentModel.DataAnnotations.EmailAddressAttribute?displayProperty=nameWithType>, <xref:System.ComponentModel.DataAnnotations.UrlAttribute?displayProperty=nameWithType>, and <xref:System.ComponentModel.DataAnnotations.PhoneAttribute?displayProperty=nameWithType>). This helps to reduce security vulnerability such as avoiding the possibility of a Denial of Service attack using specific regular expressions.<br/>
+
+In .NET Framework 4.6.1, this app setting to disable RegEx usage was set to `false` by default. Staring with .NET Framework 4.7.2, this config switch is set to `true` by default to further reduce secure vulnerability for web applications that target .NET Framework 4.7.2 and above.
+
+
+### Recommended Action
+If you find that regular expressions in your web application do not work after upgrading to .NET Framework 4.7.2, you can update the value of the `"dataAnnotations:dataTypeAttribute:disableRegEx"` setting to `false` to revert to the previous behavior.
+
+```xml
+    <configuration>
+      <appsettings>
+      ...
+        <add key="dataAnnotations:dataTypeAttribute:disableRegEx" value="false"/>
+      ...
+      </appsettings>
+    </configuration>
+```
+
+### Category
+Web Application