I was wondering when new moderators are chosen and if this information could be added to the bottom of this page.
There is no set timetable for elections--they come when we (the community) feel new/more moderators are necessary.
For some context, here's (roughly) how the most recent election (2017) came about.
This meta surfaced a number of concerns, including some with moderation. The existing moderators had already been discussing the need for another moderator--note that "we're having a mod election ASAP" was posted as an answer to "How is the community doing?" something like two minutes after the question was posted. The other moderation-related feedback confirmed the existing belief that an election would be beneficial, and off it went.
And then the election ran as you can see detailed in the /election page. Notably meta saw the 2017 Moderator Election Q&A - Questionnaire followed by voting and the 2017 Community Moderator Election Results.
If one feels that a new election is needed a meta post to that effect would be the most likely starting place.
If one feels that a regular timetable is desirable, that's a separate case to be made. (If you're considering that I'd recommend reading Should Community Moderators be "elected for life", or have terms? and many of its linked brethren before starting that conversation. This is a well-trod topic; that is not to say that it cannot be re-examined, but rather that one should clearly demonstrate familiarity with the existing consensus if they wish to be taken seriously.)