Merge branch 'document-dry-run-option' of https://github.com/Ma27/nix

doc/manual/command-ref/nix-build.xml

@@ -30,6 +30,7 @@
       <replaceable>attrPath</replaceable>
     </arg>
     <arg><option>--no-out-link</option></arg>
+    <arg><option>--dry-run</option></arg>
     <arg>
       <group choice='req'>
         <arg choice='plain'><option>--out-link</option></arg>
@@ -98,6 +99,10 @@ also <xref linkend="sec-common-options" />.</phrase></para>
 
   </varlistentry>
 
+  <varlistentry><term><option>--dry-run</option></term>
+   <listitem><para>Show what store paths would be built or downloaded</para></listitem>
+  </varlistentry>
+
   <varlistentry xml:id='opt-out-link'><term><option>--out-link</option> /
   <option>-o</option> <replaceable>outlink</replaceable></term>