docs(readme): Revamp README (#3007)
docs(readme): Revamp README (#3007)

* docs(readme): Rewrite README
* docs(readme): Fix typos and minor tweaks
* docs(readme): Add new line after CodeSandbox preview
* docs(readme): Add demo section
* docs(readme): Add playground
* docs(readme): Fix typos
* docs(readme): Fix doctoc
* docs(readme): Add Why section
* docs(readme): Rename Tourism demo to Travel
* docs(readme): Fix wording in Contributing
* docs(readme): add "we're hiring" (#3013)
* chore(readme): Peer review

algolia/instantsearch.js,algolia/instantsearch.js,algolia/instantsearch.js