docs: Add Stack Overflow question section (#759)

* Add questions section for Stack Overflow [pyhf] tag to README and FAQs

Author: matthewfeickert

README.md

@@ -111,6 +111,18 @@ To uninstall run
 python -m pip uninstall pyhf
 ```
 
+## Questions
+
+If you have a question about the use of `pyhf` not covered in [the documentation](https://scikit-hep.org/pyhf/), please ask a question on [Stack Overflow](https://stackoverflow.com/questions/tagged/pyhf) with the `[pyhf]` tag, which the `pyhf` dev team [watches](https://stackoverflow.com/questions/tagged/pyhf?sort=Newest&filters=NoAcceptedAnswer&edited=true).
+
+<p align="center">
+<a href="https://stackoverflow.com/questions/tagged/pyhf">
+<img src="https://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-logo.png" alt="Stack Overflow pyhf tag" width="50%"/>
+</a>
+</p>
+
+If you believe you have found a bug in `pyhf`, please report it in the [GitHub Issues](https://github.com/scikit-hep/pyhf/issues/new?template=Bug-Report.md&labels=bug&title=Bug+Report+:+Title+Here).
+
 ## Citation
 
 As noted in [Use and Citations](https://scikit-hep.org/pyhf/citations.html), the preferred BibTeX entry for citation of `pyhf` is

docs/faq.rst

@@ -6,6 +6,20 @@ Frequently Asked Questions about :code:`pyhf` and its use.
 Questions
 ---------
 
+Where can I ask questions about ``pyhf`` use?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If you have a question about the use of ``pyhf`` not covered in the `documentation <https://scikit-hep.org/pyhf/>`__, please ask a question on `Stack Overflow <https://stackoverflow.com/questions/tagged/pyhf>`__ with the ``[pyhf]`` tag, which the ``pyhf`` dev team `watches <https://stackoverflow.com/questions/tagged/pyhf?sort=Newest&filters=NoAcceptedAnswer&edited=true>`__.
+
+.. raw:: html
+
+  <p align="center">
+  <a href="https://stackoverflow.com/questions/tagged/pyhf">
+  <img src="https://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-logo.png" alt="Stack Overflow pyhf tag" width="50%"/>
+  </a>
+  </p>
+
+If you believe you have found a bug in ``pyhf``, please report it in the `GitHub Issues <https://github.com/scikit-hep/pyhf/issues/new?template=Bug-Report.md&labels=bug&title=Bug+Report+:+Title+Here>`__.
+
 Is it possible to set the backend from the CLI?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~