Press <C-G>c in insert mode to toggle a temporary software caps lock, or
gC in normal mode to toggle a slightly more permanent one.
If you don't have a preferred installation method, I recommend installing pathogen.vim, and then simply copy and paste:
cd ~/.vim/bundle
git clone https://github.com/tpope/vim-capslock.git
vim -u NONE -c "helptags vim-capslock/doc" -c q
Once help tags have been generated, you can view the manual with
:help capslock.
See the contribution guidelines for pathogen.vim.
Like capslock.vim? Follow the repository on GitHub and vote for it on vim.org. And if you're feeling especially charitable, follow tpope on Twitter and GitHub.
Copyright (c) Tim Pope. Distributed under the same terms as Vim itself.
See :help license.