Update 20.{1,2} docs to mention 2020 Cloud Report

[rmloveland]

Fixes #8023.

[cockroach-teamcity]

This change is 

[cockroach-teamcity]

Online preview: http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/abe0e43b2ac0a38b0d987a25025e1eba38b16329/

Edited pages:

• v20.1/performance-benchmarking-with-tpc-c-100k-warehouses.md
• v20.1/performance-benchmarking-with-tpc-c-10k-warehouses.md
• v20.1/performance-benchmarking-with-tpc-c-1k-warehouses.md
• v20.1/performance.md
• v20.2/performance-benchmarking-with-tpc-c-100k-warehouses.md
• v20.2/performance-benchmarking-with-tpc-c-10k-warehouses.md
• v20.2/performance-benchmarking-with-tpc-c-1k-warehouses.md
• v20.2/performance.md

[rmloveland]

Hey John, this is the "minimum fix" to get pages in the 20.1 and 20.2 docs pointing to the latest (2020) Cloud Report. Would appreciate your rubber stamp to make sure this looks OK. Else, please let me know if you want any changes - Thanks!

[rmloveland]

Hey @johnrk - FYI I'm gonna go ahead and merge this so we don't have the stale Cloud Report info on the site