Review updates.

+ s/CygWin/Cygwin/
+ Add a reference to the JOSS paper in `CITING.md`

Co-authored-by: Yuhsiang M. Tsai <yhmtsai@gmail.com>
Co-authored-by: Pratik Nayak <pratikvn@protonmail.com>

Author: 3 people

CHANGELOG.md

@@ -25,10 +25,10 @@ Supported systems and requirements:
   + CUDA module: CUDA 9.0+
   + HIP module: ROCm 2.8+
 + Windows
-  + MinGW and CygWin: gcc 5.3+, 6.3+, 7.3+, all versions after 8.1+
+  + MinGW and Cygwin: gcc 5.3+, 6.3+, 7.3+, all versions after 8.1+
   + Microsoft Visual Studio: VS 2017 15.7+
   + CUDA module: CUDA 9.0+, Microsoft Visual Studio
-  + OpenMP module: MinGW or CygWin.
+  + OpenMP module: MinGW or Cygwin.
 
 
 The current known issues can be found in the [known issues page](https://github.com/ginkgo-project/ginkgo/wiki/Known-Issues).
@@ -85,10 +85,10 @@ Supported systems and requirements:
   + CUDA module: CUDA 9.0+
   + HIP module: ROCm 2.8+
 + Windows
-  + MinGW and CygWin: gcc 5.3+, 6.3+, 7.3+, all versions after 8.1+
+  + MinGW and Cygwin: gcc 5.3+, 6.3+, 7.3+, all versions after 8.1+
   + Microsoft Visual Studio: VS 2017 15.7+
   + CUDA module: CUDA 9.0+, Microsoft Visual Studio
-  + OpenMP module: MinGW or CygWin.
+  + OpenMP module: MinGW or Cygwin.
 
 
 The current known issues can be found in the [known issues page](https://github.com/ginkgo-project/ginkgo/wiki/Known-Issues).

CITING.md

@@ -17,6 +17,23 @@ available through the following reference:
 Multiple topical papers exist on Ginkgo and its algorithms. The following papers
 can be used to cite specific aspects of the Ginkgo project.
 
+### The Ginkgo Software
+
+The Ginkgo software itself was reviewed and has a paper published in the Journal
+of Open Source Software, which can be cited with the following reference:
+
+```bibtex
+@article{Joss2020,
+  doi = {10.21105.joss.02260},
+  url = {https://doi.org/10.21105/joss.02260},
+  year = {2020},
+  publisher = {The Open Journal},
+  author = {Hartwig Anzt and Terry Cojean and Yen-Chen Chen and Goran Flegar and Fritz G\"{o}bel and Thomas Gr\"{u}tzmacher and Pratik Nayak and Tobias Ribizel and Yu-Hsiang Tsai},
+  title = {Ginkgo: A high performance numerical linear algebra library},
+  journal = {Journal of Open Source Software}
+}
+```
+
 ### On Portability
 
 ``` bibtex