(docu) clarify if openjdk-11 is expected to work

### Description of the problem / feature request:

I'm bootstrapping on ARM/aarch64 because there are no binaries. The [Bootstrapping docu](https://docs.bazel.build/versions/master/install-compile-source.html#bootstrap-unix) claims:

> You must install version 8 of the JDK. Versions other than 8 are not supported.

Debian (Buster) has no packages for JDK 8 (for aarch64), so I installed openjdk-11 instead. It seems to work fine.

This would be great to know in advance. The docu implies that my only option is to build JDK8 first, which would be quite an extra step.

It also claims that I need:

> EXTRA_BAZEL_ARGS="--host_javabase=@local_jdk//:jdk"

which I've omitted. The build was successful.

### What operating system are you running Bazel on?

Linux (aarch64, Debian Buster)

### What's the output of `bazel info release`?

release 3.1.0- (@non-git)

### If `bazel info release` returns "development version" or "(@non-git)", tell us how you built Bazel.

Downloaded the .zip and ran `./compile.sh` with no arguments.

### What's the output of `git remote get-url origin ; git rev-parse master ; git rev-parse HEAD` ?

not a git repository

Start with the Bootstrapping documentation at install-compile-source.html#bootstrap-unix and compare its JDK 8 requirement and EXTRA_BAZEL_ARGS guidance with the reported successful openjdk-11 build using ./compile.sh on Debian Buster aarch64. Done means the documentation clearly states whether openjdk-11 and omitting EXTRA_BAZEL_ARGS are expected to work, or preserves the existing limitation if they are not supported.

Written by the indexing model from the issue text.