Add citation recommendation

Author: amorison

README.rst

@@ -30,7 +30,16 @@ access StagYY output data directly in a Python script.
 You can install StagPy with ``pip`` from the `Python Package Index`__.
 
 This project is registered under https://doi.org/10.5281/zenodo.5512348.
-Individual DOI are also available to cite a specific version.
+Individual DOI are also available to cite a specific version.  Cite the project
+as:
+
+    Adrien Morison, Martina Ulvrova, Stephane Labrosse, & contributors. (2021).
+    StagPython/StagPy. Zenodo. https://doi.org/10.5281/zenodo.5512348
+
+or a specific version with the relevant DOI (e.g. for v0.15.0):
+
+    Adrien Morison, Martina Ulvrova, Stephane Labrosse, & contributors. (2021).
+    StagPython/StagPy (v0.15.0). Zenodo. https://doi.org/10.5281/zenodo.5512349
 
 See `the complete documentation`__ for more information on the installation and
 explanations on how to use StagPy.