Update README.md to create a Python 3.7 environment

[rcrehuet]

Current conda python version 3.10 raises the following error during the installation:

ERROR: Could not find a version that satisfies the requirement tensorflow-cpu<2.8.0 (from colabfold[alphafold]) (from versions: 2.8.0, 2.8.1, 2.8.2, 2.9.0rc0, 2.9.0rc1, 2.9.0rc2, 2.9.0, 2.9.1)
ERROR: No matching distribution found for tensorflow-cpu<2.8.0