Remove unnecessary ccpi conda dependency

Author: yousefmoazzam

.github/workflows/run_tests_iris.yml

@@ -30,7 +30,6 @@ jobs:
           environment-name: httomo_backends
           create-args: >-
             cupy==12.3.0
-            ccpi::ccpi-regulariser
           post-cleanup: 'all'
           init-shell: bash
 

README.rst

@@ -14,12 +14,23 @@ Purpose of HTTomo-backends
 Installation
 ============
 
-HTTomo-backends is available on PyPI, but currently can only be installed into a conda
-environment (due to a dependency being available only through conda).
+HTTomo-backends is available on PyPI, so it can be installed into either a virtual environment
+or a conda environment.
+
+Virtual environment
+~~~~~~~~~~~~~~~~~~~
+.. code-block:: console
+
+   $ python -m venv httomo-backends
+   $ source httomo-backends/bin/activate
+   $ pip install httomo-backends
+
+Conda environment
+~~~~~~~~~~~~~~~~~
 
 .. code-block:: console
 
    $ conda create --name httomo-backends
    $ conda activate httomo-backends
-   $ conda install -c ccpi -c conda-forge ccpi-regulariser cupy==12.3.0
+   $ conda install -c conda-forge cupy==12.3.0
    $ pip install httomo-backends