Feedback on /install: Improve discoverability

### Documentation feedback

- Page title: Install
- Page URL: https://cratedb.com/docs/guide/install/index.html
- Source: https://github.com/crate/cratedb-guide/blob/main/docs/install/index.md

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@hammerhead reported the page is currently not easy to discover, because the new "Getting started" section pulls too much attention. Also discovering it by inline search does not work, because two other pages pull too much attraction.

- https://cratedb.com/docs/sqlalchemy-cratedb/install.html
- https://cratedb.com/docs/jdbc/en/latest/getting-started.html

At least, web crawlers / search engines get it right.

- https://www.google.com/search?q=install+cratedb
- https://www.startpage.com/sp/search?q=install+cratedb

Start with docs/install/index.md and compare its navigation context with the Getting started section and the linked SQLAlchemy and JDBC pages. Investigate how these pages affect navigation and inline search, then confirm that the Install page is easier to discover without harming the linked documentation.

Written by the indexing model from the issue text.