Adjust the style of paragraph to be max-width 640px

The legibility of long paragraphs is very bad.
Please set a max-width of 640px for `sui-studio-doc-paragraph`

Thnx

Before:
![p superlong](https://user-images.githubusercontent.com/23620759/202293661-68d99ae8-9fe9-462b-9ca2-9a3dc3e71cab.png)

After enhancement:
![p enhanced](https://user-images.githubusercontent.com/23620759/202293683-572260bf-9932-48e4-827d-99a9aebe288f.png)

