You could use:
setlocal formatoptions+=a
to turn on automatic formatting of paragraphs in vim. Adding that line to the ftplugin/rst.vim
file in your vim configuration directory should do it automatically whenever you start editing a .rst
file.
If that reformats too much, it may improve things to also add the w
option. That causes vim to only consider a paragraph to extend onto the next line when a line ends with a space. It will automatically put a space at the ends of lines that are automatically inserted.