Create README.md

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

numpy/piecewise​/README.md

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+# Piecewise
+{:.no_toc}
+
+<nav markdown="1" class="toc-class">
+* TOC
+{:toc}
+</nav>
+
+## Top
+
+Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+## [numpy.piecewise](https://numpy.org/doc/stable/reference/generated/numpy.piecewise.html)
+
+```python
+numpy.piecewise(x, condlist, funclist, *args, **kw)
+```
+
+> Evaluate a piecewise-defined function.
+> 
+> Given a set of conditions and corresponding functions, evaluate each function on the input data wherever its condition is true.
+
+```python
+import numpy as np
+
+a = np.arange(1, 11)
+b = np.piecewise(a, [a < 5, a == 0, a > 5], [-1, 0, 1])
+
+print(a)  # -> [ 1  2  3  4  5  6  7  8  9 10]
+print(b)  # -> [-1 -1 -1 -1  0  1  1  1  1  1]
+```
+
+