Add alt text for social media icons

[cosimameyer]

• Add alt text for chapter table
• Add alt text for directory

Here is one place where we define the icons which might be a good starting point

[cosimameyer]

@drmowinckels I believe this issue was closed with your PR, right? 😊

[drmowinckels]

yes, I was going through my emails and I mangaed to wild-click with my mouse. This one is all sorted!