fix: address comments including BOLD references from @arokem and @josephmje

Author: oesteban

dmriprep/workflows/base.py

@@ -219,8 +219,10 @@ def init_single_subject_wf(
 
     Anatomical preprocessing is performed in a single workflow, regardless of
     the number of sessions.
-    Functional preprocessing is performed using a separate workflow for each
-    individual BOLD series.
+    Diffusion MRI preprocessing is performed using a separate workflow for
+    a full :abbr:`DWI (diffusion weighted imaging)` *entity*.
+    A DWI *entity* may comprehend one or several runs (for instance, two
+    opposed :abbr:`PE (phase-encoding)` directions.
 
     Workflow Graph
         .. workflow::

docs/usage.rst

@@ -12,7 +12,7 @@ The *dMRIPrep* workflow takes as principal input the path of the dataset
 that is to be processed.
 The input dataset is required to be in valid :abbr:`BIDS (Brain Imaging Data
 Structure)` format, and it must include at least one T1w structural image and
-(unless disabled with a flag) a BOLD series.
+(unless disabled with a flag) one :abbr:`DWI (diffusion weighted imaging)` series.
 We highly recommend that you validate your dataset with the free, online
 `BIDS Validator <http://bids-standard.github.io/bids-validator/>`_.