Added citation of the JOSS paper to the documentation

TODO.md

@@ -1,6 +1,5 @@
 TODO
 ====
-* Add the JOSS citation so people can copy it conveniently
 * Count the number of compilations and store it in the info field of the simulation
     - raise a warning when this number became too large in a simulation?
 * Think about interface for changing boundary values in numba

docs/source/manual/citing.rst

@@ -0,0 +1,36 @@
+Citing the package
+^^^^^^^^^^^^^^^^^^
+
+To cite or reference `py-pde` in other work, please refer to the `publication in
+the Journal of Open Source Software <https://doi.org/10.21105/joss.02158>`_.
+Here are the respective bibliographic records in Bibtex format:
+
+.. code-block:: bibtex
+
+    @article{py-pde,
+        Author = {David Zwicker},
+        Doi = {10.21105/joss.02158},
+        Journal = {Journal of Open Source Software},
+        Number = {48},
+        Pages = {2158},
+        Publisher = {The Open Journal},
+        Title = {py-pde: A Python package for solving partial differential equations},
+        Url = {https://doi.org/10.21105/joss.02158},
+        Volume = {5},
+        Year = {2020}
+    }
+
+and in RIS format:
+
+.. code-block:: text
+
+    TY  - JOUR
+    AU  - Zwicker, David
+    JO  - Journal of Open Source Software
+    IS  - 48
+    SP  - 2158
+    PB  - The Open Journal
+    T1  - py-pde: A Python package for solving partial differential equations
+    UR  - https://doi.org/10.21105/joss.02158
+    VL  - 5
+    PY  - 2020

docs/source/manual/index.rst

@@ -10,4 +10,5 @@ User manual
    advanced_usage
    performance
    contributing
+   citing
    code_of_conduct