docs: add pyhf compatibility

CHANGELOG.rst

@@ -8,6 +8,7 @@ Develop
 Major Features and Improvements
 -------------------------------
 - `TF-PWA <https://tf-pwa.readthedocs.io/en/latest/>`_ support for loss functions. Minimizer can directly minimize the loss function of a model.
+- `pyhf <https://pyhf.readthedocs.io/en/stable/>`_ support for loss functions. Minimizer can directly minimize the loss function of a model.
 
 Breaking changes
 ------------------

docs/api/static/zfit_physics.pyhf.rst

@@ -0,0 +1,32 @@
+pyhf
+=======================
+
+The pure Python package `pyhf <https://pyhf.readthedocs.io/en/stable/>`_ is a statistical fitting package for high energy physics for purely binned, templated fits. It is a Python implementation of the HistFactory schema.
+The connection to zfit is done via the loss function, which can be created from a pyhf model.
+
+Import the module with:
+
+.. code-block:: python
+
+    import zfit_physics.pyhf as zpyhf
+
+The loss function can be created from a ``data`` and a ``pdf`` model with
+
+.. code-block:: python
+
+    nll = zpyhf.loss.nll_from_pyhf(data, pdf)
+
+
+
+which optionally takes already created :py:class:~`zfit.core.interfaces.ZfitParameter` as arguments.
+
+
+
+
+Loss
+++++++++++++
+
+.. automodule:: zfit_physics.pyhf.loss
+    :members:
+    :undoc-members:
+    :show-inheritance: