RebaseChange: Fix typo

Change-Id: I8f8fd169ce258191b2f1fcc70e0673edb7eadc9d
Minor updates in 2.9 release notes

- The "Schema Update" section includes several warnings not related
  to schema updates.  Rename it to "Important Notes".

- Move note about removal of SQL search into "secondary index"
  section.

- Add missing periods.

Change-Id: I8ae0cc3bb8d99c711cd96812a3697b46be2a21f0
Merge branch 'stable-2.9' into stable-2.10

* stable-2.9:
  Minor updates in 2.9 release notes
  RebaseChange: Fix typo

Change-Id: If3d6656f1b31b718322d1a322bad93a98a93d256