Add readme file for the archive directory

See issue #5873

Docker-DCO-1.1-Signed-off-by: Timothy <timothyhobbs@seznam.cz> (github: https://github.com/timthelion)

archive/README.md

@@ -0,0 +1,3 @@
+This code provides helper functions for dealing with archive files.
+
+**TODO**: Move this to either `pkg` or (if not possible) to `utils`.