Does an `upload', pushing the current HEAD to the archive (as a source
package) and to dgit-repos (as git commits). The package must already
have been built ready for upload, with the .dsc and .changes
-left in the parent directory.
+left in the parent directory. It is normally best to do the build
+with dgit too (eg with dgit sbuild): some existing build tools pass
+unhelpful options to dpkg-source et al by default, which can result in
+the built source package not being identical to the git tree.
In more detail: dgit push checks that the current HEAD corresponds to
the .dsc. It then pushes the HEAD to the suite's dgit-repos branch,