docs: adds installing instruction to readme

Author: cristianoliveira

README.md

@@ -48,6 +48,12 @@ yay -S opencode-bin
 paru -S opencode-bin
 ```
 
+### Using nix flakes
+
+```bash
+nix profile install 'github:opencode-ai/opencode'
+```
+
 ### Using Go
 
 ```bash

default.nix

@@ -31,8 +31,5 @@
         homepage = "https://github.com/opencode-ai/opencode";
         mainProgram = "opencode";
         license = licenses.mit;
-        maintainers = with maintainers; [
-          zestsystem
-        ];
       };
     }