sched/doc: Document capacity aware scheduling

Add some documentation detailing the concepts, requirements and
implementation of capacity aware scheduling across the different scheduler
classes.

Signed-off-by: Valentin Schneider <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: Valentin Schneider

Documentation/scheduler/index.rst

@@ -12,6 +12,7 @@ Linux Scheduler
     sched-deadline
     sched-design-CFS
     sched-domains
+    sched-capacity
     sched-energy
     sched-nice-design
     sched-rt-group