Document constants needed to allocate scheduling contexts

[bennoleslie]

As far as I can tell the following:

/* Minimum size of a scheduling context (2^{n} bytes) */
#define seL4_MinSchedContextBits 8
#ifndef __ASSEMBLER__
/* the size of a scheduling context, excluding extra refills */
#define seL4_CoreSchedContextBytes (10 * sizeof(seL4_Word) + (6 * 8))
/* the size of a single extra refill */
#define seL4_RefillSizeBytes (2 * 8)

Are not documented in the user manual currently. However this is critical to being able to allocate a scheduling context object.

Ideally this should at least be reference in section 2.4.2 Summary of Object Sizes.

[pingerino]

Historically the seL4 manual hard coded all values and made no references to constants in seL4. I fixed this in a few places (mostly because the hard coded values were, not surprisingly, completely out of date) but not everywhere.

These constants should likely go somewhere around here: https://github.com/seL4/seL4/blob/master/manual/parts/objects.tex#L451 where the variable size of scheduling contexts is documented.