Add env vars to documentation

Readme.md

@@ -23,4 +23,15 @@ Where:
 
 ## Text indexing
 
-Not currently supported - can be supported by adding functionality to optionally include a mounted config.ttl file. This is required as the text index is not configurable via the command line.
+Not currently supported - can be supported by adding functionality to optionally include a mounted config.ttl file. This is required as the text index is not configurable via the command line.
+
+## Environment Variables
+
+| Variable | Purpose                                                                                                                                                                                                                                  | Default                                                                        | Usage Example |
+|-----------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------|----------------|
+| `DATASET` | Specifies the name of the dataset to be created                                                                                                                                                                                          | `"db"` if not set. NB: Can change name when mounting data to runtime database. | `DATASET=my_dataset` |
+| `THREADS` | Sets the number of threads to use for processing                                                                                                                                                                                         | Number of available processors minus 1                                         | `THREADS=4` |
+| `SKIP_VALIDATION` | If set, skips the validation step for RDF files                                                                                                                                                                                          | Validation is performed if not set                                             | `SKIP_VALIDATION=true` |
+| `USE_XLOADER` | If set, uses tdb2.xloader instead of tdb2.tdbloader. xloader can handle large datasets of any size. tdb2.tdbloader can only handle datasets up to a certain size (probably <100 GB, depending on the memory of the instance being used). | Uses tdb2.tdbloader if not set                                                 | `USE_XLOADER=true` |
+| `TDB2_MODE` | Specifies the loader mode for tdb2.tdbloader. See [tdbloader documentation](https://jena.apache.org/documentation/tdb2/tdb2_cmds.html) for information on available modes.                                                                                                                        | `"phased"` if not set                                                          | `TDB2_MODE=sequential` |
+| `NO_SPATIAL` | If set to true, skips the creation of a spatial index                                                                                                                                                                                    | Spatial index is created if not set                                            | `NO_SPATIAL=true` |