doc: remove trailing empty line

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
diff --git a/Makefile.custom b/Makefile.custom
index 01d69dd..c6577a5 100644
--- a/Makefile.custom
+++ b/Makefile.custom
@@ -125,6 +125,7 @@
 	$(Q)-mkdir -p docs
 	$(Q)-( \
 	    cat $(srctree)/docs/busybox_header.pod; \
+	    echo; \
 	    applets/usage_pod | sed 's/^[A-Za-z][A-Za-z ]*[a-z]:$$/&\n/'; \
 	    cat $(srctree)/docs/busybox_footer.pod; \
 	    ) > docs/busybox.pod