i18n: Correct jsdoc on how to use TranslationContext.
i18n: Correct jsdoc on how to use TranslationContext.

Thanks to @anh2111 for pointing out that these instructions
weren't right!

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile