Perf tuning follow up

[jseldess]

• Port tutorial to 2.1, retesting and updating all command output
• Calculate median instead of mean latency in Python client
• Fix download command

Addresses part of #3541.

[cockroach-teamcity]

This change is 

[cockroach-teamcity]

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/771ff3a49a6fa6f012fe29127c90faaf21bd586b/

[cockroach-teamcity]

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/02cde9717eb759e5b3d47b557bc60e34bbdc1762/

[lnhsingh]

Since it's mostly unchanged, I skimmed. LGTM, just one grammatical correction

Reviewed 1 of 16 files at r1.
Reviewable status: complete! 0 of 0 LGTMs obtained

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v2.1/performance-tuning.md, line 35 at r1 (raw file):

### Schema

You're schema and data will be based on the fictional peer-to-peer vehicle-sharing app, MovR, that was featured in the [CockroachDB 2.0 demo](https://www.youtube.com/watch?v=v2QK5VgLx6E):

"You're" -> "Your"

[jseldess]

TFTR, @lhirata.

Reviewable status: complete! 0 of 0 LGTMs obtained

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v2.1/performance-tuning.md, line 35 at r1 (raw file):

Previously, lhirata wrote…

"You're" -> "Your"

Done.

[cockroach-teamcity]

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/4edbc54e169cc98e9e54ccb3af932ae71169d24e/