M+K means M data + K parity and implies M chunks necessary to recover

Signed-off-by: Loic Dachary <loic@dachary.org>
fix typo

Signed-off-by: Loic Dachary <loic@dachary.org>
Add links to backfill related tracker items.

Signed-off-by: Loic Dachary <loic@dachary.org>
Add links to recovery related tracker items.

Signed-off-by: Loic Dachary <loic@dachary.org>
Add links to peering related tracker items.

Signed-off-by: Loic Dachary <loic@dachary.org>
Add links to scrub related tracker items.

Signed-off-by: Loic Dachary <loic@dachary.org>
Add links to OSD internals related tracker items.

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #482 from dachary/wip-erasure-coding-doc

Links to newly created tracker items, typo, M+K convention