Change: Improve installation chapter

Use the module call for pip (`python3 -m pip`) which should work on all
systems. This allows to remove the note for pip3 and restructure the
headings.

docs/install.rst

@@ -3,28 +3,21 @@
 Installation of python-gvm
 ==========================
 
-.. note:: All commands listed here use the general tool names. If some of these
-  tools are provided by the distribution, the Python 3 version of the tool may
-  have to be used, e.g. :program:`pip3`.
-
-Installing the Latest Stable Release of python-gvm
---------------------------------------------------
-
 For installing the latest stable release of **python-gvm**, `pip`_, `poetry`_
 or `pipenv`_ can be used.
 
 If an application or library that uses **python-gvm** internally is developed,
 it is often better to choose `poetry`_ for handling the dependencies.
 
 Using pip
-^^^^^^^^^
+---------
 
 For installing **python-gvm** using `pip`_ run::
 
-    pip install python-gvm
+    python3 -m pip install python-gvm
 
 Using poetry
-^^^^^^^^^^^^
+------------
 
 For installing **python-gvm** using `poetry`_ run::
 
@@ -34,7 +27,7 @@ If the usage of `poetry`_ is not familiar, its documentation can be found at
 https://python-poetry.org/docs/.
 
 Using pipenv
-^^^^^^^^^^^^
+------------
 
 For installing **python-gvm** using `pipenv`_ run::
 
@@ -55,7 +48,7 @@ To clone the public repository run::
 
 Once there is a copy of the source, it can be embedded it the own application as follows::
 
-    pip install -e /path/to/python-gvm
+    python3 -m pip install -e /path/to/python-gvm
 
 .. _pip: https://pip.pypa.io/en/stable/
 .. _pipenv: https://pipenv.readthedocs.io/en/latest/