Remove qiskit.org links (#95)

CONTRIBUTING.md

@@ -5,7 +5,7 @@
 First please read the overall project contributing guidelines. These are
 included in the Qiskit documentation here:
 
-https://qiskit.org/documentation/contributing_to_qiskit.html
+https://github.com/Qiskit/qiskit/blob/main/CONTRIBUTING.md
 
 ## Contributing to Qiskit Cold Atom
 

docs/tutorials/01_introduction_and_fermionic_circuits.ipynb

@@ -182,7 +182,7 @@
    "source": [
     "## Fermionic Gates\n",
     "\n",
-    "Quantum gates define the unitary operations that are carried out on the system. The gate unitary $U$ can be uniquely identified by the hermitian Hamiltonian $H$ that generates the evolution of the state (see [Qiskit textbook](https://qiskit.org/textbook/ch-gates/proving-universality.html#2.2-Unitary-and-Hermitian-matrices-)) as $U = e^{-i H}$.\n",
+    "Quantum gates define the unitary operations that are carried out on the system. The gate unitary $U$ can be uniquely identified by the hermitian Hamiltonian $H$ that generates the evolution of the state (see [Qiskit textbook](https://github.com/Qiskit/textbook/blob/main/notebooks/ch-gates/proving-universality.ipynb)) as $U = e^{-i H}$.\n",
     "The dynamics of cold atomic quantum simulators is commonly described by the Hamiltonian implemented by the system. The Qiskit Cold Atom module therefore defines fermionic gates using their generating Hamiltonians.\n",
     "\n",
     "As a formal language to describe fermionic Hamiltonians, we utilize the \n",

docs/tutorials/02_spin_circuits.ipynb

@@ -58,7 +58,7 @@
    "source": [
     "## Spin Gates\n",
     "\n",
-    "Quantum gates define the unitary operations that are carried out on the system. The gate unitary $U$ can be uniquely identified by the hermitian Hamiltonian $H$ that generates the evolution of the state (see [Qiskit textbook](https://qiskit.org/textbook/ch-gates/proving-universality.html#2.2-Unitary-and-Hermitian-matrices-)) as $U = e^{-i H}$.\n",
+    "Quantum gates define the unitary operations that are carried out on the system. The gate unitary $U$ can be uniquely identified by the hermitian Hamiltonian $H$ that generates the evolution of the state (see [Qiskit textbook](https://github.com/Qiskit/textbook/blob/main/notebooks/ch-gates/proving-universality.ipynb)) as $U = e^{-i H}$.\n",
     "The description of the dynamics of cold atomic quantum simulators commonly takes place on the level of the Hamiltonian which the system implements. We therefore choose a language which defines the spin gates from their generating Hamiltonians.\n",
     "\n",
     "As a formal language to describe Hamiltonians for spin systems, we utilize the \n",