Signal type package in README.md needs update

[chenspc]

Hello, I was helping a colleague debugging a hyperspy issue where he couldn't find the EDS signal type. The readme says it's built-in, but after some digging, it appears that EDS_TEM now belongs to exspy. After installing exspy, I can see it with print_known_signal_types().

DielectricFunction, EDS_SEM, and EELS are also part of exspy. I suspect hologram is now part of holospy, but haven't tested myself.

One small suggestion is to include the simple conda install xxx (and/or pip equivalent) instruction lines to README.md, as opposed to building an environment from a .txt file. Some new users may not be familiar with this approach.

Thanks!

[ericpre]

Indeed this is out of date, because the workflow supposed to update it (https://github.com/hyperspy/hyperspy-extensions-list/actions/workflows/update_readme.yml) doesn't work - kikuchipy doesn't support hyperspy 2.0 which makes the script fail.

[jlaehne]

Resolved in #62