Document installing borgmatic with pip install --user instead of a system Python install.

docs/how-to/develop-on-borgmatic.md

@@ -41,7 +41,7 @@ you're in the `borgmatic/` working copy, install tox, which is used for
 setting up testing environments:
 
 ```bash
-sudo pip3 install tox
+pip3 install --user tox
 ```
 
 Finally, to actually run tests, run:

docs/how-to/set-up-backups.md

@@ -7,16 +7,24 @@ To get up and running, first [install
 Borg](https://borgbackup.readthedocs.io/en/latest/installation.html), at
 least version 1.1.
 
-Then, run the following command to download and install borgmatic:
+Borgmatic consumes configurations in `/etc/borgmatic/` and `/etc/borgmatic.d/`
+by default. Therefore, we show how to install borgmatic for the root user which
+will have access permissions for these locations by default.
+
+Run the following commands to download and install borgmatic:
 
 ```bash
-sudo pip3 install --upgrade borgmatic
+sudo pip3 install --user --upgrade borgmatic
 ```
 
+This is a [recommended user site
+installation](https://packaging.python.org/tutorials/installing-packages/#installing-to-the-user-site).
+You will need to ensure that `/root/.local/bin` is available on your `$PATH` so
+that the borgmatic executable is available.
+
 Note that your pip binary may have a different name than "pip3". Make sure
 you're using Python 3, as borgmatic does not support Python 2.
 
-
 ### Other ways to install
 
 Along with the above process, you have several other options for installing

docs/how-to/upgrade.md

@@ -7,7 +7,7 @@ In general, all you should need to do to upgrade borgmatic is run the
 following:
 
 ```bash
-sudo pip3 install --upgrade borgmatic
+sudo pip3 install --user --upgrade borgmatic
 ```
 
 See below about special cases.
@@ -25,14 +25,14 @@ already running borgmatic with Python 3, then you can upgrade borgmatic
 in-place:
 
 ```bash
-sudo pip3 install --upgrade borgmatic
+sudo pip3 install --user --upgrade borgmatic
 ```
 
 But if you were running borgmatic with Python 2, uninstall and reinstall instead:
 
 ```bash
 sudo pip uninstall borgmatic
-sudo pip3 install borgmatic
+sudo pip3 install --user borgmatic
 ```
 
 The pip binary names for different versions of Python can differ, so the above
@@ -67,7 +67,7 @@ from atticmatic to borgmatic by running the following commands:
 
 ```bash
 sudo pip3 uninstall atticmatic
-sudo pip3 install borgmatic
+sudo pip3 install --user borgmatic
 ```
 
 That's it! borgmatic will continue using your /etc/borgmatic configuration