DOC: lib: Use a clearer example of ddof in the notes of the cov docstring.
DOC: lib: Use a clearer example of ddof in the notes of the cov docstring.

Use `ddof = 1` instead of 9, and remove a confusing comment.

Closes gh-15010.

madphysicist/numpy,rgommers/numpy,grlee77/numpy,numpy/numpy,numpy/numpy,abalkin/numpy,seberg/numpy,charris/numpy,WarrenWeckesser/numpy,jakirkham/numpy,pbrod/numpy,WarrenWeckesser/numpy,anntzer/numpy,pbrod/numpy,madphysicist/numpy,numpy/numpy,seberg/numpy,madphysicist/numpy,WarrenWeckesser/numpy,charris/numpy,mhvk/numpy,abalkin/numpy,mattip/numpy,pdebuyl/numpy,anntzer/numpy,simongibbons/numpy,simongibbons/numpy,jakirkham/numpy,WarrenWeckesser/numpy,rgommers/numpy,charris/numpy,endolith/numpy,mhvk/numpy,pbrod/numpy,anntzer/numpy,pbrod/numpy,pdebuyl/numpy,madphysicist/numpy,mhvk/numpy,madphysicist/numpy,endolith/numpy,pbrod/numpy,grlee77/numpy,anntzer/numpy,pdebuyl/numpy,seberg/numpy,mhvk/numpy,simongibbons/numpy,rgommers/numpy,endolith/numpy,seberg/numpy,jakirkham/numpy,grlee77/numpy,rgommers/numpy,grlee77/numpy,mattip/numpy,charris/numpy,numpy/numpy,jakirkham/numpy,mhvk/numpy,mattip/numpy,jakirkham/numpy,pdebuyl/numpy,endolith/numpy,simongibbons/numpy,abalkin/numpy,grlee77/numpy,mattip/numpy,WarrenWeckesser/numpy,simongibbons/numpy