Improve 'service' command

Add a way to add file descriptor arguments to a call, and document the
previously undocumented 'null' command.

Test: manual
Change-Id: I561092d40f5036c8f42d65fefd0da85cd9164c5f
diff --git a/cmds/service/Android.bp b/cmds/service/Android.bp
index 9513ec1..a5b1ac5 100644
--- a/cmds/service/Android.bp
+++ b/cmds/service/Android.bp
@@ -4,6 +4,7 @@
     srcs: ["service.cpp"],
 
     shared_libs: [
+        "libcutils",
         "libutils",
         "libbinder",
     ],
@@ -22,6 +23,7 @@
     srcs: ["service.cpp"],
 
     shared_libs: [
+        "libcutils",
         "libutils",
         "libbinder",
     ],