PR Summary

The shape of a 2D array is (nrows, ncols), but images are normally described by width x height (ncols, nrows). The docstring for imshow() had these a bit mixed up in my opinion. This clarifies it.

I'm not sure if the default is to use (m, n) or (n, m) to represent the shape of a 2D array. Grepping through the project reveals roughly equal use of both. I've left it as (m, n) in this PR, but maybe we should do another PR to make the notation consistent throughout the project.

PR Checklist

• Has Pytest style unit tests
• Code is PEP 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way