Update README to use a Docker image matching the one used in CI.

[niting]

The local test reproduction on docker, as specified in the README, fails currently with the following error:

error[E0133]: access to union field is unsafe and requires unsafe function or block
--> src/ioctls/vm.rs:1331:9
|
1331 | irqchip.chip.pic.irq_base = 10;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior

This PR fixes the local test failure by appropriately marking the code as unsafe.

[andreeaflorescu]

Hey @niting. For some reason in the CI that unsafe doesn't yield an error. Maybe it is because of the rust version, or something else. I can look into it next week. Sorry for the late reply.

[niting]

Thank you for looking into it! This indeed was an older toolchain issue - the particular error was fixed in rust-lang/rust#42083 and I confirmed that this doesn't happen anymore with the newer version of the Docker image. I have accordingly updated the commit. I am not sure why coverage runs still fail on the commit.

[andreeaflorescu]

Coverage on arm is pretty much random at this point. I'll update the CI to skip that test until we find out what's happening there. You can also manually update to the value it expects.

To merge this PR, can you please sign your commit?
git commit --amend -s --no-edit

Thanks.

[niting]

Done, thanks! I went ahead and signed the commit but skipped the manual update.

[niting]

@andreeaflorescu and @aghecenco thank you for the reviews. Do I need to update the test coverage for the PR to be merged? Or does it require an additional review?

[andreeaflorescu]

@niting I'll open a PR to drop that coverage-arm test. We'll merge that one first, then update the branch for this one, then merge it.

I just didn't got around to open that PR just yet :))

We'll be doing that soon. No action required from your part. Thanks!