Create README.md

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

numpy/flat/README.md

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+# flat
+{:.no_toc}
+
+<nav markdown="1" class="toc-class">
+* TOC
+{:toc}
+</nav>
+
+## Top
+
+Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+## [numpy.ndarray.flat](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.flat.html)
+
+```python
+ndarray.flat
+```
+
+> A 1-D iterator over the array.
+> 
+> This is a numpy.flatiter instance, which acts similarly to, but is not a subclass of, Python’s built-in iterator object.
+
+```python
+import numpy as np
+
+a = np.arange(0, 12).reshape((4, 3))
+c = np.zeros_like(a)
+
+print(a)
+print()
+
+for i in range(0, c.size):
+    c.flat[i] = a.flat[i] ** 2
+
+print(c)
+```
+
+Output:
+
+```python
+[[ 0  1  2]
+ [ 3  4  5]
+ [ 6  7  8]
+ [ 9 10 11]]
+
+[[  0   1   4]
+ [  9  16  25]
+ [ 36  49  64]
+ [ 81 100 121]]
+```
+
+## Reminder: size vs shape
+
+### [numpy.ndarray.size](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.size.html#numpy-ndarray-size)
+
+```python
+ndarray.size
+```
+
+> Number of elements in the array.
+> 
+> Equal to np.prod(a.shape), i.e., the product of the array’s dimensions.
+
+### [ndarray.shape](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.shape.html#numpy-ndarray-shape)
+
+```python
+ndarray.shape
+```
+
+> Tuple of array dimensions.
+
+