Add discussion of LIBS_FROM_GIT

Add a pointer to installing clients via LIBS_FROM_GIT to local.conf
sample.  Mention in the git tree setup that the projects within are
usually installed via released pip versions.

Change-Id: I245094e51ea4a8ce983f6a1e48b6ab7ca5d309d0
diff --git a/stackrc b/stackrc
index 23a4a7c..cfdcd4d 100644
--- a/stackrc
+++ b/stackrc
@@ -268,6 +268,7 @@
 ##############
 #
 #  OpenStack Client Library Components
+#   Note default install is from pip, see LIBS_FROM_GIT
 #
 ##############
 
@@ -317,6 +318,7 @@
 ###################
 #
 #  Oslo Libraries
+#   Note default install is from pip, see LIBS_FROM_GIT
 #
 ###################