Packages required for building on Debian 9

[Samathy]

Debian 9 is pretty old now, but castget builds okay if you install the following packages:

pkg-config
libglib2.0-dev
libxml2-dev
libcurl3-dev
libid3-dev

( and obviously make and a c compiler )

Happy to make a PR to get that written down, but this project seems to have pretty limited 'build' instructions for specific OSs so I'd like advice on where is best to put this package list.

[BorisWilhelms]

Similar for Alpine (e.g. when building in docker) you need to install the following packages:

• libxml2-dev
• glib-dev
• curl-dev
• taglib-dev

[mlj]

Thanks, I'll add this to the README.md file.

It's going to be challenging to keep this up to date over time since I don't regularly test on any of these platforms. The CI builds use Ubuntu + MacOS, so those two I can keep up to date, but for others I would appreciate help keeping an eye on things :)

Re. the list for Debian 9: The development version has switched from id3lib to taglib. Based on this, it looks like libtagc0-dev is the required dependency, but would be great if somebody can confirm.