Update source/core/indexes.txt

Added index caveats wrt $or
initial cut of mongoperf doc
DOCS-999 draft reorg landing page
DOCS-999 reorg landing page w table and Stack Overflow
DOCS-996 modifying reference pages to be well formed
draft port of the smoke tests doc from the wiki.
rst cleanup
DOCS-969 correcting cross referecnces and fixing potential linking problems
merge: minor smoke test edits
merge: corrections
merge: DOCS-999 reorganization
DOCS-999 reorganization edits and tweaks
DOCS-999: edits to table processing
DOCS-987 break up shard page into concepts, tutorials, refs
DOCS-987 break out sharding-requirements into own page
DOCS-987 change link format on shard page, create shard command ref
DOCS-987 many changes
DOCS-987 ongoing
DOCS-987 ongoing
DOCS-987 semi-solution for administration/sharding doc