add: can now keep local custom user rc file ./skippy-xd.rc in-repo

[dreamcat4]

This changes should not conflict with any other recent ongoing / pending work. It merely adds capability to

add: can now keep local custom user rc file ./skippy-xd.rc in-repo (this custom user file is .gitignored)

if found / detected (optional file exists) --> then make install will give priority and install it into /etc/xdg/ if not found (default) --> then make install will just copy the default sample rc instead (as always)

example usage:

$ make
$ cp ./skippy-xd.sample.rc ./skippy-xd.rc

# edit your skippy-xd.rc file in-repo, it will be ignored by git

$ sudo make install
your custom skippy config file will be installed to: /etc/xdg/skippy-xd.rc
install -m 644 skippy-xd.rc "/etc/xdg/skippy-xd.rc"
skippy's sample config file will be installed to: /etc/xdg/skippy-xd.sample.rc
install -m 644 skippy-xd.sample.rc "/etc/xdg/skippy-xd.sample.rc"

Possible missing functionality / limitation:

• if you want to instead put a symlink from another location (outside your working tree). So that it is then picked up into your local working tree. Then install command might just copy the symlink itself, rather than follow where the symlink goes, to copy the source file elsewhere in other location.

[dreamcat4]

hi, @felixfung please pull back to your local repo my changes, to keep in sync with master. for easier rebase / merge. It's just minor thing here, should not affect any of your own work.