Added synb0 explanation to documentation

Author: salimansourc

docs/sdc.rst

@@ -18,3 +18,17 @@ Correction Methods
   5. nonlinear registration
 
   6. synthetic b0
+  
+  The synb0 method is based off of this `paper <https://www.sciencedirect.com/science/article/abs/pii/S0730725X18306179/>`_. It offers an alternative method of SDC by using deep learning on an anatomical image (T1).
+  
+  You can use it in this pipeline by generating the synb0s for the subject(s) and passing the bids-like directory containing them to the --synb0_dir parameter. To find out how to generate the synb0s, you can visit our `forked repo <https://github.com/TIGRLab/Synb0-DISCO>`_.
+  
+  Once you have a directory of synb0s (recommended to place as derivatives of bids folder, ex. bids/derivatives/synb0/sub-XX), then you are ready to run the pipeline using them! Just run dmripreproc as you usually would, with bids_dir and output_dir, but now add "--synb0_dir <your_synb0_directory>" to your command. 
+    
+  The synb0 acqp for topup and eddy will be automatically generated in the pipeline in the following format:
+  
+  0 -1 0 <total_readout_time>
+  
+  0 1 0 0
+  
+  If you want to overwrite the total_readout_time with one of your own, simply add "--total_readout <new_trt_time>" to your command.