filter-repo only consists of a few files that need to be installed:

  * git-filter-repo

    This can be installed in the directory pointed to by `git --exec-path`,
    or placed anywhere in $PATH.  This is the only thing needed for basic use.

  * git_filter_repo.py

    If you want to make use of one of the scripts in contrib/filter-repo-demos/,
    or want to write your own script making use of filter-repo as a python
    library, then you need to have a symlink to (or copy of) git-filter-repo
    named git_filter_repo.py in $PYTHONPATH.

  * git-filter-repo.1

    If you want `git filter-repo --help` to display the manpage, this needs
    to be copied into $MANDIR/man1/ where $MANDIR is some entry from $MANPATH.

  * git-filter-repo.html

    The manpage is good enough for me and my systems, but an html-formatted
    version of the same page is provided for those who prefer it.  Place it
    where ever you like; I have no idea where such a thing should go.

Installing should be doable by hand, but a Makefile is provided for those
that prefer it.  However, usage of the Makefile really requires overridding
at least a couple of the directories with sane values, e.g.

    $ make prefix=/usr pythondir=/usr/lib64/python3.8/site-packages install