docs: document which CamSIS envs Digital Pooling services use

docs/services/digital-pooling.md

@@ -198,6 +198,17 @@ The flow of applicant data to/from the SMI and other services is summarised by t
 
 ![Flow of applicant data to/from the SMI](subject-moderation-interface-data-flow.jpg)
 
+### CamSIS environments
+
+The following relationship holds between Digital Pooling environments and CamSIS environments:
+
+| Digital Pooling env | CamSIS env |
+|---------------------|------------|
+| development         | intb_dat   |
+| test (staging)      | intb_test  |
+| integration         | intb_reg   |
+| production          | intb_prod  |
+
 ## Service Management and tech lead
 
 The **service owner** for Digital Pooling is Helen Reed.