Update pyRiemann-qiskit.toml (#729)

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### Summary
Add missing documentation to `.toml` file.


### Details and comments

ecosystem/resources/members/pyRiemann-qiskit.toml

@@ -7,3 +7,4 @@ affiliations = "pyRiemann (https://github.com/pyRiemann)"
 labels = [ "Machine learning",]
 stars = 21
 group = "applications"
+documentation = "https://pyriemann-qiskit.readthedocs.io/"