Recommend updating pip in installation doc

Newer versions of `pip` no longer require the `--user` switch.

Author: amorison

docs/sources/developers.rst

@@ -27,7 +27,7 @@ Testing
 StagPy uses tox_ for code testing.  Make sure it is installed and up to date on
 your system::
 
-    % python3 -m pip install -U --user tox
+    % python3 -m pip install -U tox
 
 .. _tox: https://tox.readthedocs.io
 
@@ -41,7 +41,7 @@ Documentation
 The StagPy documentation is built with Sphinx_. To build it locally, install
 and update the needed packages::
 
-    % python3 -m pip install -U --user sphinx sphinx-rtd-theme
+    % python3 -m pip install -U sphinx sphinx-rtd-theme
 
 .. _Sphinx: https://www.sphinx-doc.org
 

docs/sources/install.rst

@@ -21,9 +21,13 @@ module to install it (it is bootstrapped within the Python interpreter)::
 In case this doesn't work, download the official script
 <https://bootstrap.pypa.io/get-pip.py> and run it with ``python3``.
 
+Then, update ``pip`` to the latest version::
+
+    % python3 -m pip install -U --user pip
+
 You can then install and/or update StagPy with the following command::
 
-    % python3 -m pip install -U --user stagpy
+    % python3 -m pip install -U stagpy
 
 Make sure that the directory where ``pip`` install package entry-points
 (usually ``~/.local/bin``) is in your ``PATH`` environment variable.