Instalation improvements

[dvdmc]

• Indicate that detectron2 is also required for FastSAM
• In case of using a virtualenv, it is required to install rospkg

I can add both and do a pull request with your okay :)

[dvdmc]

Additionally, pytorch / torchvision ... etc are listed in requirements.txt
The problem with this approach is that probably it will be installed for an uncompatible CUDA version. Normally, pytorch should be installed manually through:
https://pytorch.org/get-started/locally/

Example in:
https://docs.nerf.studio/quickstart/installation.html#pytorch