Clarify usage of GELI rc.d script.

PR:		docs/187321
Reviewed by:	Allan Jude and mat@ on IRC

en_US.ISO8859-1/books/handbook/disks/chapter.xml

@@ -3126,8 +3126,8 @@ Filesystem     Size   Used  Avail Capacity  Mounted on
 geli_da2_flags="-p -k /root/da2.key"</programlisting>
 
 	<para>This configures <filename>/dev/da2</filename> as a
-	  <command>geli</command> provider of which the master key
-	  file is located in <filename>/root/da2.key</filename>.
+	  <command>geli</command> provider with a master key
+	  file of <filename>/root/da2.key</filename>.
 	  <command>geli</command> will not use a passphrase when
 	  attaching to the provider if
 	  <option>-P</option> was given during the
@@ -3135,6 +3135,26 @@ geli_da2_flags="-p -k /root/da2.key"</programlisting>
 	  the <command>geli</command> provider from the kernel before
 	  the system shuts down.</para>
 
+	<note>
+	  <para>During the startup process, scripts prompt for the
+	    passphrase before attaching the <acronym>GELI</acronym>
+	    provider.  Other kernel messages might be shown before and
+	    after the password prompt.  If the boot process seems to
+	    stall, look carefully for the password prompt among the
+	    other messages.</para>
+
+	  <para>When the correct password is given, the provider is
+	    attached.  A consumer, like a file system, is then mounted
+	    on the provider, typically by an entry in
+	    <filename>/etc/fstab</filename> (see
+	    &man.fstab.5;).</para>
+
+	  <para>Later in the startup process, &os; configures
+	    <acronym>GELI</acronym> providers to automatically detach.
+	    <acronym>GELI</acronym> providers without any consumers
+	    will detach at that time.</para>
+	</note>
+
 	<para>More information about configuring
 	  <filename>rc.d</filename> is provided in the
 	  <link linkend="configtuning-rcd">rc.d</link> section of the