Installation instructions adapted to the requirement cftime>=1.5. (#4260

)

* Installation instructions adapted to the requirement cftime>=1.5.

* pip installation instructions simplified

* typo fixed

* installation instructions shortened

* whatsnew

* unnecessary blank spaces removed

docs/src/installing.rst

@@ -52,29 +52,17 @@ this section are valid for Debian-based Linux distributions (Debian, Ubuntu,
 Kubuntu, etc.).
 
 Iris and its dependencies need some shared libraries in order to work properly.
-These can be installed
-with apt::
+These can be installed with apt::
 
   sudo apt-get install python3-pip python3-tk libudunits2-dev libproj-dev proj-bin libgeos-dev libcunit1-dev
 
-Consider executing::
+The rest can be done with pip::
 
-  sudo apt-get update
-
-before and after installation of Debian packages.
-
-The rest can be done with pip. Begin with numpy::
-
-  pip3 install numpy
-
-Finally, Iris and its Python dependencies can be installed with the following
-command::
-
-  pip3 install setuptools cftime==1.2.1 cf-units scitools-iris
+  pip3 install scitools-iris
 
 This procedure was tested on a Ubuntu 20.04 system on the
-27th of January, 2021.
-Be aware that through updates of the involved Debian and/or Python packages,
+26th of July, 2021.
+Be aware that through updates of the involved Debian packages,
 dependency conflicts might arise or the procedure might have to be modified.
 
 .. _installing_from_source:

docs/src/whatsnew/latest.rst

@@ -136,6 +136,9 @@ This document explains the changes made to Iris for this release
    a conda development environment. See :ref:`installing_from_source`.
    (:pull:`4240`)
 
+#. `@MHBalsmeier`_ updated and simplified non-conda installation on Debian-based distros.
+   (:pull:`4260`)
+
 
 💼 Internal
 ===========