doc: Update actions regards to the hook post-files

[silvio]

In #600 you can read that the post-files-hook is only executed for certain commandos. I think this is worth to be documented.

[markkrj]

Even better, it would be good if it was actually supported... As I said, build-lxc do create a rootfs tarball, but it also install lxc stuff into it. It would be cool if we could use distrobuilder to build a golden rootfs tarball that could be used for bootstrapping a VM, for example.

[monstermunchkin]

As I said, build-lxc do create a rootfs tarball, but it also install lxc stuff into it.

@markkrj Right. But you can run distrobuilder build-dir which gives you a rootfs directory. You could then use tar to make a tarball.

[markkrj]

But, why is post-files not supported for build-dir?

[monstermunchkin]

But, why is post-files not supported for build-dir?

The build-dir command is primarily used for preparing a build directory before running pack-lxc or pack-lxd which both support running post-files. However, it would make sense to also support post-files in build-dir. Since I don't want to change the current behaviour, I'm considering adding a new --with-post-files flag to build-dir.