lsp server not started properly

I hit the following error: https://github.com/huggingface/llm.nvim/blob/7657d65adac2901b4712f73d81d5827d7c0494f4/lua/llm/language_server.lua#L116
1/ I think the message could be improved, aka "no LSP server enabled for this buffer"
2/ LspInfo gives me:
```
Client: llm-ls (id: 1, bufnr: [1, 6])
filetypes:
autostart: false
root directory: /home/teto/nixpkgs
cmd: /nix/store/ngay8qxw0bnirwsnjsk84bdcsbd2q9kc-llm-ls-0.4.0/bin/llm-ls
```
which means the config here https://github.com/huggingface/llm.nvim/blob/7657d65adac2901b4712f73d81d5827d7c0494f4/lua/llm/language_server.lua#L189 is probably not enough (it should autostart maybe ?).
Turns out `:LspStart llm-ls` seems to start it (I see "codellama currently loading", ~~I hope it's not too long~~ took 1mn and I could accept the proposition with the binding in `accept_keymap`).

Interested in adding llm-ls to https://github.com/neovim/nvim-lspconfig ? ping me if you open a PR and I can review it.