Document how to handle multiple paths for QIBOLAB_PLATFORMS

[andrea-pasquale]

Qibolab is able to handle multiple paths in the environment variable QIBOLAB_PLATFORMS.

qibolab/src/qibolab/_core/platform/load.py

Lines 17 to 26 in 9a2b1c6

	def _platforms_paths() -> list[Path]:
	"""Get path to repository containing the platforms.
	Path is specified using the environment variable QIBOLAB_PLATFORMS.
	"""
	paths = os.environ.get(PLATFORMS)
	if paths is None:
	raise_error(RuntimeError, f"Platforms path ${PLATFORMS} unset.")
	return [Path(p) for p in paths.split(os.pathsep)]

However, this feature is not documented since all examples in the documentation are referring to a single path. This could be relevant soon for some ongoing PRs in qibocal: qiboteam/qibocal#1103 qiboteam/qibocal#1101