bug#40478: feature request/idea: guix pull --news should show information about new package replacements

[Jack Hill]

Hi Guix,

I'm an avid reader of `guix pull --news`. I like learning about new and 
updated software. However, I noticed that when a package gains a new 
replacement (e.g. for a security fix via grafting), it is not mentioned. 
We do not show all changes to package definitions in the new, but since a 
new replacement is often for a security fix, I think it is significant 
enough to warrant showing in the news. I'm imagining something like:

"""
n packages with new replacements: gnutls, …
"""

or perhaps:

"""
n packages with new grafts: libxml, …
"""

I haven't yet though about the implementation of this. I would want to 
avoid doing too much extra work for `guix pull --news`.

What do you think?

Best,
Jack