Issue 25224: Augment Idle doc feature list and no-subprocess section

to finish making current README.txt obsolete.

Lib/idlelib/help.html

@@ -80,10 +80,15 @@
 <ul class="simple">
 <li>coded in 100% pure Python, using the <tt class="xref py py-mod docutils literal"><span class="pre">tkinter</span></tt> GUI toolkit</li>
 <li>cross-platform: works on Windows, Unix, and Mac OS X</li>
+<li>Python shell window (interactive interpreter) with colorizing
+of code input, output, and error messages</li>
 <li>multi-window text editor with multiple undo, Python colorizing,
-smart indent, call tips, and many other features</li>
-<li>Python shell window (a.k.a. interactive interpreter)</li>
-<li>debugger (not complete, but you can set breakpoints, view and step)</li>
+smart indent, call tips, auto completion, and other features</li>
+<li>search within any window, replace within editor windows, and search
+through multiple files (grep)</li>
+<li>debugger with persistent breakpoints, stepping, and viewing
+of global and local namespaces</li>
+<li>configuration, browsers, and other dialogs</li>
 </ul>
 <div class="section" id="menus">
 <h2>24.6.1. Menus<a class="headerlink" href="#menus" title="Permalink to this headline">¶</a></h2>
@@ -503,6 +508,15 @@ set in the Options dialog.</li>
 </div>
 <div class="section" id="running-without-a-subprocess">
 <h3>24.6.4.2. Running without a subprocess<a class="headerlink" href="#running-without-a-subprocess" title="Permalink to this headline">¶</a></h3>
+<p>By default, Idle executes user code in a separate subprocess via a socket,
+which uses the internal loopback interface.  This connection is not
+externally visible and no data is sent to or received from the Internet.
+If firewall software complains anyway, you can ignore it.</p>
+<p>If the attempt to make the socket connection fails, Idle will notify you.
+Such failures are sometimes transient, but if persistent, the problem
+may be either a firewall blocking the connecton or misconfiguration of
+a particular system.  Until the problem is fixed, one can run Idle with
+the -n command line switch.</p>
 <p>If IDLE is started with the -n command line switch it will run in a
 single process and will not create the subprocess which runs the RPC
 Python execution server.  This can be useful if Python cannot create