Create README.md

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

numpy/slices_views/README.md

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+# Slices and views
+{:.no_toc}
+
+<nav markdown="1" class="toc-class">
+* TOC
+{:toc}
+</nav>
+
+## The goal
+
+Sometimes we want to use or see only a part of the matrix. This can be done via slices and views
+
+Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+## Reminder 
+
+We assume N as the number of elements and 1d:​
+
+* A valid index starts at **0** and runs until N-1​
+* [start:stop:step] ​
+    start = 1, stop=N, step=1 ​-> this results in the sequence​ 1,2,3,...,(N-1)​
+* [start:stop:1] can be shortened to [start:stop]​
+* [0:stop] can be shortened to [:stop]​
+* [start:N] can be shortened to [start:]​
+* B = A[:] or B = A[...] gives you a view of A. B has the same shape and size of A. ​
+
+```python
+import numpy as np
+
+a = np.arange(0, 10)
+print(a[1:10:1])  # -> [1 2 3 4 5 6 7 8 9]
+print(a[3:7:2])  # -> [3 5]
+print(a[3:6])  # -> [3 4 5]
+print(a[:6])  # -> [0 1 2 3 4 5]
+print(a[5:])  # -> [5 6 7 8 9]
+print(a[:])  # -> [0 1 2 3 4 5 6 7 8 9]
+print(a[...])  # -> [0 1 2 3 4 5 6 7 8 9]
+```