README: Rename "Packaging" -> "Source Packaging"

Should be less confusing for binary-package maintainers.

Change-Id: I60ded87c9665a51343b284ef7ae5a58021896c3e
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/222
diff --git a/README.md b/README.md
index 3f73923..607f772 100644
--- a/README.md
+++ b/README.md
@@ -20,8 +20,8 @@
 Please see the flashprog(8) manpage.
 
 
-Packaging
----------
+Source Packaging
+----------------
 
 To package flashprog and remove dependencies on Git, either use
 make export