Add a more detailed SCHED_DEADLINE description
Few corrections to the real-time tasks section
Mention admission control where appropriate

The CBS guarantee can only be provided if a proper admission control
is enforced... Mention this as early as possible.
Change "depleted" in "throttled"

"throttled" is more in line with the Linux kernel naming. Anyway,
keep a reference to the term commonly used in literature.
Fix a cut'n'paste typo
Introduce the "replenishment time" concept
Merge pull request #1 from lucabe72/dl-doc

Dl doc