nixos boot doc: document boot.debug1devices

nixos/doc/manual/administration/boot-problems.xml

@@ -38,6 +38,17 @@
      </para>
     </listitem>
    </varlistentry>
+   <varlistentry>
+    <term>
+     <literal>boot.debug1devices</literal>
+    </term>
+    <listitem>
+     <para>
+      Like <literal>boot.debug1</literal>, but with some more devices loaded.
+      This may help with e.g. making the keyboard work.
+     </para>
+    </listitem>
+   </varlistentry>
    <varlistentry>
     <term>
      <literal>boot.trace</literal>