doc: Increase the free storage requirement for building to 65 GBytes

Issue-Id: SCM-3318
Signed-off-by: Diego Sueiro <diego.sueiro@arm.com>
Change-Id: I569e5ed1d3dffa482b167a3b6c6aaa3cb4aa228f
8 jobs for v0.1.1 in 26 seconds (queued for 11 seconds)
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