ja: Japanese translation doesn't have a section of "Availability in numbers" which exists in English version

There is no section on "Availability in numbers" in the Japanese translation even though the section exists in the English version.

English https://github.com/donnemartin/system-design-primer#availability-in-numbers

Japanese https://github.com/donnemartin/system-design-primer/blob/master/README-ja.md#%E5%8F%AF%E7%94%A8%E6%80%A7%E3%83%91%E3%82%BF%E3%83%BC%E3%83%B3