Create README.md

Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>

numpy/nested_iters/README.md

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+# zip
+{:.no_toc}
+
+<nav markdown="1" class="toc-class">
+* TOC
+{:toc}
+</nav>
+
+## Top
+
+Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+{: .topic-optional}
+This is an optional topic!
+
+## [numpy.nested_iters](https://numpy.org/doc/stable/reference/generated/numpy.nested_iters.html)
+
+```python
+numpy.nested_iters(op, axes, flags=None, op_flags=None, op_dtypes=None, order='K', casting='safe', buffersize=0)
+```
+
+> Create nditers for use in nested loops
+> 
+> Create a tuple of nditer objects which iterate in nested loops over different axes of the op argument. The first iterator is used in the outermost loop, the last in the innermost loop. Advancing one will change the subsequent iterators to point at its new element.
+
+```python
+import numpy as np
+
+
+a = np.arange(1, 7).reshape((2, 3))
+print(a)
+print()
+
+iter_a, iter_b = np.nested_iters(a, [[0], [1]], flags=["multi_index"])
+
+for x in iter_a:
+    for y in iter_b:
+        print(
+            f"iter_a.multi_index: {iter_a.multi_index}, iter_b.multi_index: {iter_b.multi_index}"
+        )
+```
+
+Output:
+
+```python
+[[1 2 3]
+ [4 5 6]]
+
+iter_a.multi_index: (0,), iter_b.multi_index: (0,)
+iter_a.multi_index: (0,), iter_b.multi_index: (1,)
+iter_a.multi_index: (0,), iter_b.multi_index: (2,)
+iter_a.multi_index: (1,), iter_b.multi_index: (0,)
+iter_a.multi_index: (1,), iter_b.multi_index: (1,)
+iter_a.multi_index: (1,), iter_b.multi_index: (2,)
+```