Fix broken links in documentation.

[patrickdavey]

This fixes a few broken links. One of which (the overview-of-exercism link) seems like it should now point to the overview-architecture page, which is what I've made it do.

Thanks for the great website! Love Exercism!

[patrickdavey]

Thanks @kytrinyx . I fixed the link and pushed it back up (altering the commit message to remove the part about the link I wasn't sure about). I did force push it up.. I thought an extra commit would just be extra noise.

[kytrinyx]

Sweet, thanks for the quick turnaround on this! 🌷