Update announcing-sourcegraph-3.7.md
Created by: slimsag
- Do not mention opting out, that is not a useful property (and more likely to cause issues than benefits for anyone).
- 6,000 repos/hr was inaccurate, 1,400 repos/hr is the corrected number.
- Link to benchmarks, mention 20x speedup of large symbol searches.
- Replace alert section with link to 3.7.2+ migration guide.
- Remove mention of monitoring via https://sourcegraph.example.com/site-admin/repositories?filter=needs-index -- that no longer works in 3.7.2. See migration guide for how to monitor.
- Remove mention of 30% disk space increase, in 3.7.2 it is now 130% increase since we retain old index version. Migration guide mentions this.
- Remove memory increase mention, migration guide covers this better mentioning gains we made in 3.6 which negate this.