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MINOR: [C++][Docs] Adds link in "Using Arrow C++ in your own project" to Arrow install page (#13808)

Currently, users of the C++ documentation have to go find the commands and availability for installing Arrow in their package manager of choice themselves. While this is only a small irritation, it's easily fixed by adding a link to the install page. This PR adds said link.

Authored-by: Kae S <31679808+ksuarez1423@users.noreply.github.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>