Right way: define, build and install

[Jone]

On Gentoo I actively used github: download, then local build and install
in ~/{bin,tools}. It was easy! I didn't even need ebuilds and did not
think as this works :-)

Now I need several applications which are absent and will not be in
official repositories of a distribution. For an example:
1. https://github.com/x2b/usbeject
2. xfce4-cpugraph-plugin

I tried to define this as "some-package.scm" and build, but the first
requires some magic with gexp, and for the second - it is unknown what
for "use-modules". Finally, in the manual is just one stupid example
"hello"!

Help!!