doc: mention how to install with the rocks.nvim plugin manager

rocks.nvim takes care of dependencies for you.

Author: teto

README.md

@@ -231,6 +231,18 @@ For building binary if you wish to build from source, then `cargo` is required.
 
 </details>
 
+<details>
+
+  <summary><a href="https://github.com/lumen-oss/rocks.nvim">rocks.nvim</a></summary>
+
+Run `:Rocks install avante.nvim` then add to your init.lua:
+
+```lua
+require('avante').setup()
+```
+
+</details>
+
 <details>
 
   <summary>vim-plug</summary>