Added a README

apps/cli/executables/go/gmva_ingester/README.md

+# gmva_ingester
+
+`gmva_ingester` is a utility that copies GMVA observation directories from the
+GMVA source directory (defined in CAPO) to the VLBI ingestion staging directory
+(also defined in CAPO). It is not meant to be run by hand, but by a workflow
+that facilitates the entire GMVA observation ingestion process.
+
+# Usage
+```
+Usage of ./gmva_ingester:
+  -dir string
+        Name of the GMVA directory within the GMVA source directory to be copied to the VLBI staging directory
+```