[no ci] docs: add basic likelihood estimation example

Fixes #476. This is the barebones version showing the technical steps to
do likelihood estimation. Adding more background and motivation would be
nice.

Author: vpratz

docsrc/source/examples.rst

@@ -18,3 +18,4 @@ The corresponding Jupyter Notebooks are available :mainbranch:`here <examples/>`
    _examples/From_ABC_to_BayesFlow.ipynb
    _examples/One_Sample_TTest.ipynb
    _examples/Lotka_Volterra_Point_Estimation_and_Expert_Stats.ipynb
+   _examples/Likelihood_Estimation.ipynb