Update installation instructions to support binary installer:
Update installation instructions to support binary installer:

- Updates install.md to include information on downloading and running the installer
- Updates getting-started.md to refer users to the installation instructions

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MOS_MIGRATED_REVID=101943813

bazelbuild/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website