docs: zstd

[j23414]

Description of proposed changes

For the zika, measles, and dengue s3 endpoints; switch from xz and gz to the faster zstd to be consistent with:

• https://github.com/nextstrain/ncov-ingest/pull/345

Filled in details to measles and dengue instructions, to be consistent with zika instructions.

Related issue(s)

Related to:

• https://github.com/nextstrain/ncov-ingest/pull/345

Related PRs:

• https://github.com/nextstrain/dengue/pull/5
• https://github.com/nextstrain/measles/pull/7
• https://github.com/nextstrain/zika/pull/23

Testing

• [x] Checks pass

Any proof-reading is welcome! Or edits to the wording.