INSTALL: streamline a bit and guide folks to package managers

Now that several package managers are packaging filter-repo (Debian and
Ubuntu seem to be the primary holdouts, but maybe treating Linux as
"covered" will pressure them to package it too), guide people to use
package managers for easy installation and streamline the wording.
Still keep the old instructions around, just move them later.

Signed-off-by: Elijah Newren <newren@gmail.com>

INSTALL.md

@@ -1,4 +1,22 @@
-# What/why/where to install things
+# Installation via Package Manager
+
+Installation is as easy as
+
+    $ PACKAGE_TOOL install git-filter-repo
+
+for those using one of the following [package
+managers](https://alternativeto.net/software/yellowdog-updater-modified/?license=opensource)
+to install software on their system:
+
+[![Packaging status](https://repology.org/badge/vertical-allrepos/git-filter-repo.svg)](https://repology.org/project/git-filter-repo/versions)
+
+This list covers at least Windows (Scoop), Mac OS X (Homebrew), and
+Linux (most the rest).  Note that I do not curate this list (and have
+no interest in doing so); https://repology.org tracks who packages
+these versions.
+
+
+# Manual Installation
 
 filter-repo only consists of a few files that need to be installed:
 
@@ -33,19 +51,6 @@ filter-repo only consists of a few files that need to be installed:
     where ever you like; I have no idea where such a thing should go.
 
 
-# Installation via Makefile
-
-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
-
-Also, the Makefile will not edit the shebang line (the first line) of
-git-filter-repo if your python executable is not named "python3";
-you'll still need to do that yourself.
-
-
 # Installation via [pip](https://pip.pypa.io/)
 
 For those who prefer to install python packages via pip, you merely need
@@ -54,24 +59,14 @@ to run:
     $ pip3 install git-filter-repo
 
 
-# Installation via Package Manager
-
-For those who prefer to install software via a [package
-manager](https://alternativeto.net/software/yellowdog-updater-modified/?license=opensource)
-for their operating system, there are many choices -- from
-[dnf](https://github.com/rpm-software-management/dnf) or
-[yum](http://yum.baseurl.org/) or
-[apt-get](https://www.debian.org/doc/manuals/debian-reference/ch02.en.html)
-or whatever for Linux, to [brew](https://brew.sh/) for Mac OS X, to
-[scoop](https://scoop.sh/) for Windows.  Nearly any of these tools
-will reduce the installation instructions down to
+# Installation via Makefile
 
-    $ PACKAGE_TOOL install git-filter-repo
+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.
 
-I have no interest in tracking all these pre-built packages (nor
-whether those who packaged git-filter-repo have made modifications or
-left parts of it out), but apparently https://repology.org is willing
-to track who has packaged it.  So, using repology's packaging status
-link, the following package managers have packaged git-filter-repo:
+    $ make prefix=/usr pythondir=/usr/lib64/python3.8/site-packages install
 
-[![Packaging status](https://repology.org/badge/vertical-allrepos/git-filter-repo.svg)](https://repology.org/project/git-filter-repo/versions)
+Also, the Makefile will not edit the shebang line (the first line) of
+git-filter-repo if your python executable is not named "python3";
+you'll still need to do that yourself.