README.md and Bootstrap cleanup

[jgfoster]

• Update README.md links to 11.0
• Use defaults for BUILD_NUMBER and BOOTSTRAP_ARCH if not provided (no need to require them)
• Provide Dockerfile example
• Remove instructions for adding 32-bit libraries to Docker container
• Remove previous VM so we don't get an error if the bootstrap is rerun
• Use the latest VM for the bootstrap

[astares]

@jgfoster Why do you switch to 11 (leaving out 10). Usually the last stable (Pharo 10 at the moment) should be used, as Pharo 11 is alpha and a moving target still. No?

[jgfoster]

@astares, that's a good question and to be honest I didn't think about it very much; I just assumed that it should be the latest. But now, having thought about it, I think I can make a case for '11'.

• The "Download Pharo" link talks about a "stable version" and this leads visitors to the Launcher download which will give a choice of versions. So people who are just looking for Pharo will use the Launcher.
• Given that the changes are made to a README.md in a branch named Pharo11, I think it makes sense for the "latest build" to point to the latest build of Pharo11. This is especially true when discussing the Bootstrap process—any bootstrap from this branch will create a Pharo11 image.

But, my primary interest is in the bootstrap process and if you think it would be better for the Pharo11 branch to point to the latest build of Pharo10, I won't quibble; mostly I appreciate getting some feedback!

[astares]

Maybe @guillep can give some feedback here

[MarcusDenker]

Failing test is not related:

• SpJobListPresenterTest>>testJobIsFinishedWhenWaitingMoreThanWorkBlockDuration

[MarcusDenker]

Lots of people are on holidays right now, so reviewing is a bit slower than in normal times

[jgfoster]

@guillep , @astares , Any further comments or requests?

[Ducasse]

Guille is on vacation for two weeks