Automatic port of JsonElement.GetRawText remarks (#3945)

Author: carlossanlop

xml/System.Text.Json/JsonElement.xml

@@ -652,7 +652,15 @@ If a property is defined multiple times for the same object, the method matches
       <Docs>
         <summary>Gets a string that represents the original input data backing this value.</summary>
         <returns>The original input data backing this value.</returns>
-        <remarks>To be added.</remarks>
+        <remarks>
+          <format type="text/markdown"><![CDATA[
+
+## Remarks
+
+If the <xref:System.Text.Json.JsonElement> instance is built from a <xref:System.Text.Json.JsonNode>, the value of <xref:System.Text.Json.JsonNode.ToJsonString> is returned.
+
+          ]]></format>
+        </remarks>
         <exception cref="T:System.ObjectDisposedException">The parent <see cref="T:System.Text.Json.JsonDocument" /> has been disposed.</exception>
       </Docs>
     </Member>