[shotwell] Add comment to prevent plugin install problems later

[Jim Nelson <jnelson src gnome org>]

commit 3007b2ec2a450034e5bc97d7d03df02ab10778fe
Author: Jim Nelson <jim yorba org>
Date:   Tue May 6 13:58:53 2014 -0700

    Add comment to prevent plugin install problems later

 plugins/shotwell-publishing-extras/Makefile |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/plugins/shotwell-publishing-extras/Makefile b/plugins/shotwell-publishing-extras/Makefile
index f310d4c..9259fbb 100644
--- a/plugins/shotwell-publishing-extras/Makefile
+++ b/plugins/shotwell-publishing-extras/Makefile
@@ -19,6 +19,7 @@ SRC_FILES := \
        ../../src/util/string.vala \
        ../common/RESTSupport.vala
 
+# RC_FILES must also be added to ../plugins.mk to ensure they're installed properly
 RC_FILES := \
        gallery3.png \
        gallery3_authentication_pane.glade \