Positioning: Change link text to be descriptive about curriculum

[MaoShizhong]

Thanks for opening this issue, @Crn0. This can knock out one of the lessons for an upcoming issue like the foundations links one you contributed to, before we finalise everything and open the large issue.

Could proposed change 1 be amended slightly to have:

- It might sound confusing, but checking out the behavior of [this](https://codepen.io/theanam/pen/MPLBYy) example might clear things up for you.
+ It might sound confusing, so check out this [example of sticky positioning](https://codepen.io/theanam/pen/MPLBYy).

And then add another fix for line 50:

- [This MDN article](https://developer.mozilla.org/en-US/docs/Web/CSS/position) covers all of the conceptual details about positioning.
+ [MDN's docs on `position`](https://developer.mozilla.org/en-US/docs/Web/CSS/position) covers all of the conceptual details about positioning.

The other 3 proposed changes are 🤌

[Crn0]

Thank you for the suggestions, Mao!

I just noticed that I forgot to include Assignment 3 in the previous list, and I also forgot to include the proposed changes for Assignment 2. How silly of me >.<