Improve documentation

[FynnBe]

Add examples to the docs motivated by bioimage-io/core-bioimage-io-python#445 (comment)

TODO:

• add more examples to other parts of the spec!

[github-actions]

☂️ Python Coverage

current status: ❌

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
4935	2470	50%	70%	🔴

New Files

File	Coverage	Status
bioimageio/spec/_internal/node_converter.py	86%	🔴
TOTAL	86%	🔴

Modified Files

File	Coverage	Status
bioimageio/spec/_internal/init.py	100%	🟢
bioimageio/spec/_internal/common_nodes.py	48%	🔴
bioimageio/spec/_internal/types.py	74%	🟢
bioimageio/spec/generic/v0_3.py	77%	🟢
bioimageio/spec/model/v0_4.py	65%	🟢
bioimageio/spec/model/v0_5.py	45%	🔴
TOTAL	68%	🔴

updated for commit: 63de066 by action🐍