Fix https://github.com/scylladb/scylla-doc-issues/issues/864 This PR: - updates the introduction to add information about AArch64 and rewrite the content. - replaces "Scylla" with "ScyllaDB". Closes #11778 * github.com:scylladb/scylladb: Update docs/getting-started/system-requirements.rst doc: fix the link to the OS Support page doc: replace Scylla with ScyllaDB doc: update the info about supported architecture and rewrite the introduction