add debian packaging related information

Using the debian directory in this commit, it is possible to generate
libosmocore and libosmocore-dev packages (dpkgs).
diff --git a/debian/libosmocore.dirs b/debian/libosmocore.dirs
new file mode 100644
index 0000000..e168dc6
--- /dev/null
+++ b/debian/libosmocore.dirs
@@ -0,0 +1,5 @@
+usr/lib
+usr/include
+usr/include/osmocore
+usr/include/osmocom
+usr/include/osmocom/vty