Merge branch 'mnt/fslpy_warning' into 'master'

MNT: warning about fslpy practical

See merge request fsl/pytreat-practicals-2020!16

advanced_topics/08_fslpy.md

 # `fslpy`
 
+# THIS IS A WORK IN PROGRESS - DO NOT READ
+
+
 `fslpy` is a Python library which is built into FSL, and contains a range of
 functionality for working with neuroimaging data in an FSL context.