Update version of python referenced in README.rst installation instructions (#1307)

* new version of python

* add reminder to change directory (in case this is relevant)

Author: tbhallett

README.rst

@@ -21,8 +21,8 @@ Please use the `Installation Guide <https://github.com/UCL/TLOmodel/wiki/Install
 you prefer, you can carry out the setup using the command line:
 
 ::
-
-    conda create -n tlo python=3.8
+    cd TLOmodel
+    conda create -n tlo python=3.11
     conda activate tlo
     pip install -r requirements/dev.txt
     pip install -e .