Blueberry needs an update

[vgazioglu]

Since Blueberry has been replaced by Blueman, I think the related documentaion in the below page needs to be updated.

https://linuxmint-developer-guide.readthedocs.io/en/latest/xapps.html

[nekomajin]

Link to the blog post of the announcement: https://blog.linuxmint.com/?p=4323

[SkylarLK]

I wrote an update in my upcoming pull request.