Add example workflow for UMI following primer

[Jason Vander Heiden]

We could use either a small example or a full workflow for data where the UMI is after the primer region (using MaskPrimers-extract).

Example protocol:

Turchaninova, M. A. et al. High-quality full-length immunoglobulin profiling with unique molecular barcoding. Nat. Protoc. 11, 1599–1616 (2016).

Though, that might just be a case of using the TS site as the primer: CTTGGGG