docs: change Linaro release version to 20.01

We currently use Linaro release software stack version
20.01 in the CI. Reflect that change in the docs.

Signed-off-by: Zelalem Aweke <zelalem.aweke@arm.com>
Change-Id: I0fa9f0163afb0bf399ec503abe9af4f17231f173
2 files changed