Identifying the current path and assigning a dedicated font

[shahryarjb]

To begin, I'd like to extend my gratitude for all of the efforts you've put in. 🌹

As a result of my experience, I have 3 recommendations about the creation of some tutorials in LiveBook.

1. in other languages, such as Persian, we need to set a special font for the description; otherwise, it won't even be possible to understand what's written on a single page, and users would simply pass over it and give up on the chapter. It is not user-friendly and has only a very small size.
2. When using the Mac version, the user can open the index.livemd file anywhere in his system; however, the LiveBook is unable to recognize the path from which it was opened. As a result, if we have some files in the same folder as the index.livemd file, such as in the "/datasets folder, the user will see the message no such file or directory. Absolute path can be used to remedy it, but new users are not aware of this feature and hence cannot alter the block code.
3. The RTL layout is not supported by LiveBook by default. For those of us whose first language is not English, having an option that is similar to GitHub Markdown, if it is even possible, would be helpful.

[josevalim]

Thanks for the feedback! Pull requests to address item 1 and 3 will be welcome. :)

Regarding step 2, you can retrieve the current directory relative to .livemd by using __DIR__.