doc

- develop.txt is for design/guidelines; architecture/concepts should
  live elsewhere (currently src/nvim/README.md)
- move dev-jargon to intro.txt
- replace https://neovim.io/community (deprecated) with
  https://neovim.io/#chat
- <Cmd> avoids CmdlineEnter/Leave
  https://github.com/vim/vim/issues/2889

src/nvim/api/vim.c

@@ -743,6 +743,9 @@ void nvim_err_writeln(String str)
 
 /// Gets the current list of buffer handles
 ///
+/// Includes unlisted (unloaded/deleted) buffers, like `:ls!`.
+/// Use |nvim_buf_is_loaded()| to check if a buffer is loaded.
+///
 /// @return List of buffer handles
 ArrayOf(Buffer) nvim_list_bufs(void)
   FUNC_API_SINCE(1)