Update mthree URL (#807)

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Closes #806

ecosystem/resources/members/mthree.toml

@@ -1,5 +1,5 @@
 name = "mthree"
-url = "https://github.com/Qiskit-Extensions/mthree"
+url = "https://github.com/Qiskit/qiskit-addon-mthree"
 description = "Matrix-free Measurement Mitigation (M3). Reduce the effects of readout errors from noisy quantum hardware."
 licence = "Apache 2.0"
 contact_info = ""
@@ -10,5 +10,5 @@ created_at = 1678827878.805163
 updated_at = 1678827878.805164
 stars = 37
 group = "other"
-documentation = "https://qiskit-extensions.github.io/mthree/"
+documentation = "https://qiskit.github.io/qiskit-addon-mthree"
 uuid = "875968b2-f9e9-44a9-a5dc-4db9c4805021"