It doesn't seem that vimhelp.org includes the man page for Vim... It looks like they're only serving and indexing the Vim :help
files instead.
You can find the man page for Vim in its GitHub repository, it seems that besides the nroff vim.1
source code for the man page, they actually include a text rendering for it under file vim.man
.
The man page is also not really directly accessible from Vim's :help
system, since they're essentially separate. The most closely related contents to those found in the man page, including a description of command-line arguments, can be found under :help starting
.