lightline integration

### Description

I guess https://github.com/catppuccin/nvim/pull/949 also means integrations for plugins like `lightline` also stop working.
(of course people can probably migrate from `lightline` to `lualine`, but they have to know)

If this is intended (and I guess it is), we should also update the [*integrations* section of the `README.md`](https://github.com/catppuccin/nvim?tab=readme-ov-file#integrations)

### Neovim version

```markdown
NVIM v0.12.1
Build type: RelWithDebInfo
LuaJIT 2.1.1774896198
Run "nvim -V1 -v" for more info
```

### Terminal and multiplexer

st with tmux (but not really relevant here)

### Catppuccin version / branch / rev

426dbeb

### Steps to reproduce

none, it's about the docs

### Expected behavior

none, it's about the docs

### Actual behavior

none, it's about the docs

### Repro

```Lua
not relevant here
```