I would go even further: Our primitive ancestors likely descended from proto-humans that descended from primates that were already foraging eggs. Some modern apes and other mammals eat eggs as well, we've likely been eating eggs since hundreds of thousands of years before the first human evolved.
In a sense, that line of though is interesting: When we think of "observing other animals eating something, and then deciding to eat it", we're almost implicitly forgetting that we are descendants of exactly those types of animals, that "just know" what is safe to eat, and that some of the knowledge we have about food is potentially passed down from even before the first primates evolved.
When exactly did our ancient ancestors observe that eggs come from a creature's ass, and decide 'hey, this is okay to eat, let's make it a daily breakfast'?
Exactly! I mean.. some reptiles eat eggs, so we could be talking about something that happened before our ancestors had developed the concept of an ass. I don't think it's far-fetched to think that eating eggs may be as old a concept as eggs themselves. In that case, the first egg-eaters evolved alongside the first egg-layers, and were eating proto-eggs before even the modern egg existed.
Imagine if zebras started evolving very tough placentas over time, and the foals started lying around in them for a couple days before popping out: Lions would keep eating newborn zebras, and no single lion generation would notice that they were slightly different from 1000 years prior. Give that development a million years or whatever and you now have egg-laying zebras and egg-eating lions!
Nearly every animal will eat an egg given the right oppourtunity. It makes sense given it has everything needed to create a new animal. The same goes for milk for mammals.
Again, more speculation, but maybe our ancient ancestors stumbled on some random eggs already cooked from a natural forest fire, and then thought 'hey, this fire stuff seems useful'...