docs(macos): update links according to HCI guidelines for improved readability

[coolaj86]

Preview

See the changes in action at:

https://github.com/coolaj86/tinygo-site/blob/patch-1/content/getting-started/install/macos.md

Here, here!

I changed the links by

• making the visual target much larger by making the text of the links more specific and clear
• placing links closer to the beginning or end of the sentence rather than in the middle
• using strict markdown link indicators <>

As general (and highly effective) HCI / Technical Writing / Accessibility guidelines, the words "this", "here", "click", etc should be hunted down and vanquished! (and replaced with action phrases / content descriptions)

The Colors Duke, The Colors!

I'm a superchromat (i.e. perfect color / hue distinction), on a Macbook (nearly perfect hue/color display), and the difference between the space black text and dark grey blue links is so difficult to distinguish that I couldn't recognize the links as such.

I'd highly recommend changing both the unvisited and visited link colors and adding underlines to at least links in text bodies.

[deadprogram]

@coolaj86 I think this is an excellent set of changes. Any chance you could give the same treatment to the other getting-started pages? 😸