toaster-manual: Updated the section for setting up virtual env.

The section for setting up a Python virtual environment has
gone from "optional" to "required".  I re-worded the section
as such.

(From yocto-docs rev: 3a20244c8b0b594723c0b35c8808bb96a210d63a)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/toaster-manual/toaster-manual-start.xml

@@ -41,16 +41,16 @@
             install-compatible format.
         </para>
 
-        <section id='toaster-optional-virtual-environment'>
+        <section id='toaster-virtual-environment'>
-            <title>Optionally Setting Up a Python Virtual Environment</title>
+            <title>Set Up a Python Virtual Environment</title>
 
             <para>
-                It is highly recommended that you use a Python virtual
+                Set up a Python virtual environment that allows you
-                environment that allows you to maintain a dedicated Python
+                to maintain a dedicated Python executable and its own
-                executable and its own set of installed modules.
+                set of installed modules.
-                Doing so separates the executable from the Python and modules
+                Doing so separates the executable from Python and the
-                provided by the operating system and therefore avoids any
+                modules provided by the operating system.
-                version conflicts.
+                This separation avoids any version conflicts.
             </para>
 
             <para>
@@ -73,7 +73,7 @@
                         </para></listitem>
                 </orderedlist>
                 <note>
-                    If you do choose to set up a virtual environment in
+                    After setting up a virtual environment in
                     which to run Toaster, you must initialize that
                     virtual environment each time you want to start
                     Toaster.