Uses python -m pip style for installation

Updates the readme to use `python -m pip install` style for
installing python packages. This is what we suggest at upstream
to reduce the confusion of which Python interpreter is being used.

See more: https://snarky.ca/why-you-should-use-python-m-pip/

README.md

@@ -13,11 +13,11 @@ AudioCraft requires Python 3.9, PyTorch 2.0.0. To install AudioCraft, you can ru
 ```shell
 # Best to make sure you have torch installed first, in particular before installing xformers.
 # Don't run this if you already have PyTorch installed.
-pip install 'torch>=2.0'
+python -m pip install 'torch>=2.0'
 # Then proceed to one of the following
-pip install -U audiocraft  # stable release
-pip install -U git+https://[email protected]/facebookresearch/audiocraft#egg=audiocraft  # bleeding edge
-pip install -e .  # or if you cloned the repo locally (mandatory if you want to train).
+python -m pip install -U audiocraft  # stable release
+python -m pip install -U git+https://[email protected]/facebookresearch/audiocraft#egg=audiocraft  # bleeding edge
+python -m pip install -e .  # or if you cloned the repo locally (mandatory if you want to train).
 ```
 
 We also recommend having `ffmpeg` installed, either through your system or Anaconda: