Add remark about MaxConnectionsPerServer (#8450)

Author: rzikm

xml/System.Net.Http/SocketsHttpHandler.xml

@@ -608,7 +608,18 @@ Timeout must be greater than or equal to 1 second. Set to <xref:System.Threading
       <Docs>
         <summary>Gets or sets the maximum number of simultaneous TCP connections allowed to a single server.</summary>
         <value>The maximum number of simultaneous TCP connections allowed to a single server.</value>
-        <remarks>To be added.</remarks>
+        <remarks>
+          <format type="text/markdown"><![CDATA[  
+
+In this context, server means a unique combination of
+
+- IDN host name (as used in the request URI)
+- Port
+- Value of the Host HTTP header (if present, e.g. when HTTPS is used)
+- URI of the HTTP Proxy (if proxy is used).
+
+         ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="MaxResponseDrainSize">