articles/vi.md: update article

articles/vi.md

@@ -1,10 +1,23 @@
 # vi
-vi is a family of text editors originated in Berkley and first included in
+vi is a family of **vi**sual text editors originated in [BSD](bsd.md) [Unix](unix.md).
-[BSD](bsd.md) [Unix](unix.md).
+
+In contrast to most editors, vi is a modal editor, in which its behavior depends on the current
+mode that is in. For example, the starting mode is the *normal* mode in which vi accept
+commands; the *insert* mode, where vi accepts keys and writes them to the current buffer; the
+*replacement* mode, similar to insert mode but replaces the characters under the cursor instead of
+adding them to the buffer; the *visual* mode which allows for selection of text.
+
+## Tutorial
+Vim provides a tutorial, accesible through the `vimtutor` *shell* command; Neovim provides the same
+tutorial with the `:Tutor` *editor* command.
+
+TODO
 
 ## vi-like editors
 - Vim: vi improved, one of the most popular vi-like editors; includes a scripting language,
-VimScript, for extending the editor.
+VimScript for extending the editor.
-- Neovim: a fork of Vim, adds [Lua](lua.md) as a replacement for VimScript.
+- Neovim: a fork of Vim, adds [Lua](lua.md) as a replacement for VimScript, improves performance.
 - nvi: reimplementation of the original Berkley vi, is the default `vi` editor in the [BSDs](bsd.md).
+- vis: minimalistic vi-like editor, adds structured regular expressions inspired by the [Sam](sam.md) and
+[Acme](acme.md) editors, includes Lua for scripting.
 - ...