[sysprof] build: add some scary warning messages

[Christian Hergert <chergert src gnome org>]

commit c2cafc9882bb14bc7d5f40d854ba6d4294c56cf6
Author: Christian Hergert <christian hergert me>
Date:   Sun Apr 24 17:23:04 2016 -0700

    build: add some scary warning messages

 configure.ac |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index ac34f2c..8559597 100644
--- a/configure.ac
+++ b/configure.ac
@@ -259,8 +259,15 @@ echo "    The sysprofd system daemon provides support"
 echo "    for accessing hardware performance counters"
 echo "    as a normal user."
 echo ""
+echo "    ** Without this, whole-system capture will **"
+echo "    ** require running as root.                **"
+echo ""
 echo "  Systemd System Units ......................... : ${with_systemdsystemunitdir}"
 echo ""
 echo "    sysprofd uses systemd to manage the service"
 echo "    and sd-bus for D-Bus communication."
 echo ""
+echo "    ** Make sure this is somewhere that systemd **"
+echo "    ** can locate your service files, or the UI **"
+echo "    ** will not be able to elevate privileges.  **"
+echo ""