WinForms - Update xml doc Dock = DockStyle.Fill is the default

Make it clear we are setting the default to DockStyle.Fill, this may not be expected
by some. It has been that way for 5+ years, so changing the default would be difficult
and unexpected, instead we make it clearer this is the case.

Resolves cefsharp#3019

Author: amaitland

CefSharp.WinForms/ChromiumWebBrowser.cs

@@ -416,21 +416,25 @@ public ChromiumWebBrowser()
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ChromiumWebBrowser"/> class.
+        /// **Important** - When using this constructor the <see cref="Control.Dock"/> property
+        /// will default to <see cref="DockStyle.Fill"/>.
         /// </summary>
         /// <param name="html">html string to be initially loaded in the browser.</param>
-        /// <param name="requestContext">Request context that will be used for this browser instance,
-        /// if null the Global Request Context will be used</param>
+        /// <param name="requestContext">(Optional) Request context that will be used for this browser instance, if null the Global
+        /// Request Context will be used.</param>
         public ChromiumWebBrowser(HtmlString html, IRequestContext requestContext = null) : this(html.ToDataUriString(), requestContext)
         {
 
         }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ChromiumWebBrowser"/> class.
+        /// **Important** - When using this constructor the <see cref="Control.Dock"/> property
+        /// will default to <see cref="DockStyle.Fill"/>.
         /// </summary>
         /// <param name="address">The address.</param>
-        /// <param name="requestContext">Request context that will be used for this browser instance,
-        /// if null the Global Request Context will be used</param>
+        /// <param name="requestContext">(Optional) Request context that will be used for this browser instance, if null the Global
+        /// Request Context will be used.</param>
         public ChromiumWebBrowser(string address, IRequestContext requestContext = null)
         {
             Dock = DockStyle.Fill;