Provide docker instructions in install.md

[jeremyfowers]

docs/install.md doesn't mention installing docker, but as soon as you get started you run into this:

(mla) azureuser@benchtest:~/mlagility$ benchit examples/cli/scripts/hello_world.py

Models discovered during profiling:

hello_world.py:
    pytorch_model (executed 1x)
        Model Type: Pytorch (torch.nn.Module)
        Class:      SmallModel (<class 'hello_world.SmallModel'>)
        Location:   /home/azureuser/mlagility/examples/cli/scripts/hello_world.py, line 30
        Parameters: 60 (<0.1 MB)
        Hash:       2a1e15ca
        Status:     Unknown benchit error: Docker installation not found. Please install Docker>=20.10

install.md should make sure that users have docker installed before sending them on to the tutorials.

[jeremyfowers]

cc @ramkrishna2910