Fix ffmpeg install command

[aliberts]

What this does

Fix ffmpeg install command

[theo-michel]

Careful this might have broken my conda for some reason !

[shantanuparab-tr]

Here's what i have noticed.

Running

conda install ffmpeg -c conda-forge -y

Before

pip install --no-binary=av -e .

Causes issue while building pyav form source. This won't be noticed if you have even 1 successful build of pyav on your system as miniconda will use the cached version of that build. To recreate this issue you can run

pip install --no-binary=av -e . --no-cached-dir --force-reinstall

Changing the order of these steps help avoid the issue, without any noticeable issue further down the process. Steps that work.

1. Install Lerobot
2. Install ffmpeg

[aliberts]

Superseded by #903