`add` command should not look for other files in repository

I have a .git folder in the root directory. When I do `rgit add <somfile>` the operation with the following error:
```shell
$ rgit add a.txt 
thread 'main' panicked at src/workspace.rs:102:71:
failed to read file: Error { kind: InvalidData, message: "stream did not contain valid UTF-8" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```