README: use apt-get --assume-yes in Dockerfile

[Minoru]

This little change makes it even easier for someone to create their own Dockerfile: they simply copy an example and start listing the packages they need. Without --assume-yes, apt-get install will try to interactively ask for confirmation, and fail since docker build runs it in a non-interactive environment.

[reitermarkus]

I think all other occurrences are using -y.

[Minoru]

@reitermarkus I don't really know, I've seen all of the three aliases. I personally think docs should use long options so people don't have to look them up. Then the choice is between --yes and --assume-yes. Now that I think about it, I don't know why I'm always using the latter, but it's just how it is.

I'm okay with changing it to anything else if a reviewer asks for it.

[reitermarkus]

The main point is that we should be consistent. Feel free to change all Dockerfiles and scripts to use the long option as well.

[Minoru]

Ah, sorry, I somehow misunderstood you and though that you're talking of all the Dockerfiles in existence, not just the ones in this repo. I've changed them all to use --assume-yes as well.

The "real" Dockerfiles in this repo also use --no-install-recommends, but I decided not to add it to README since the user might actually want recommended packages. The goal of this PR is simply to make the example work out of the box.

[Minoru]

CI error doesn't look related to my changes at all.

[reitermarkus]

bors try

[bors]

try

Build failed:

• rust-embedded.cross

[reitermarkus]

bors retry

[bors]

try

Build succeeded:

• rust-embedded.cross

[reitermarkus]

bors r+

[bors]

Build succeeded:

• rust-embedded.cross

[reitermarkus]

Thanks, @Minoru!