vim: enable folds but don't automatically close them
The command to have no folds closed when a buffer is opened is
:set foldlevelstart=99
See
:help foldlevelstart
for more.
you can do:
set nofoldenable
for example in my .vimrc I have:
set foldmethod=indent " automatically fold by indent level
set nofoldenable " ... but have folds open by default