home-manager: pass -L/--print-build-logs to nix build

When building from a flake, `nix build` hides the build output by
default, with a `-L`/`--print-build-logs` option to show it. Pass this
option along from `home-manager` if the user provides it.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

docs/man-home-manager.xml

@@ -155,6 +155,18 @@
     --keep-going
    </arg>
 
+   <arg>
+    <group choice="req">
+     <arg choice="plain">
+      -L
+     </arg>
+
+     <arg choice="plain">
+      --print-build-logs
+     </arg>
+    </group>
+   </arg>
+
    <arg>
     --show-trace
    </arg>
@@ -546,6 +558,22 @@
      </para>
     </listitem>
    </varlistentry>
+   <varlistentry>
+    <term>
+     <option>-L</option>
+    </term>
+    <term>
+     <option>--print-build-logs</option>
+    </term>
+    <listitem>
+     <para>
+      Passed on to <citerefentry>
+      <refentrytitle>nix build</refentrytitle>
+      </citerefentry>
+      when building from a flake.
+     </para>
+    </listitem>
+   </varlistentry>
    <varlistentry>
     <term>
      <option>--show-trace</option>