Update the README

README.md

@@ -28,18 +28,32 @@ Or install it yourself as:
 ## Usage
 
 ### Converting metadata
-
+#### Converting metadata into GeoBlacklight JSON
+GeoCombine provides several classes representing different metadata standards that implement the `#to_geoblacklight` method for generating records in the [GeoBlacklight JSON format](https://opengeometadata.org/reference/):
+```ruby
+GeoCombine::Iso19139 # ISO 19139 XML
+GeoCombine::OGP # OpenGeoPortal JSON
+GeoCombine::Fgdc # FGDC XML
+GeoCombine::EsriOpenData # Esri Open Data Portal JSON
+GeoCombine::CkanMetadata # CKAN JSON
+```
+An example for converting an ISO 19139 XML record:
 ```ruby
 # Create a new ISO19139 object
 > iso_metadata =  GeoCombine::Iso19139.new('./tmp/opengeometadata/edu.stanford.purl/bb/338/jh/0716/iso19139.xml')
 
-# Convert ISO to GeoBlacklight
+# Convert to GeoBlacklight's metadata format
 > iso_metadata.to_geoblacklight
 
-# Convert that to JSON
+# Output it as JSON instead of a Ruby hash
 > iso_metadata.to_geoblacklight.to_json
+```
+Some formats also support conversion into HTML for display in a web browser:
+```ruby
+# Create a new ISO19139 object
+> iso_metadata =  GeoCombine::Iso19139.new('./tmp/opengeometadata/edu.stanford.purl/bb/338/jh/0716/iso19139.xml')
 
-# Convert ISO (or FGDC) to HTML
+# Convert ISO to HTML
 > iso_metadata.to_html
 ```
 
@@ -69,7 +83,7 @@ id_map = {
 GeoCombine::Migrators::V1AardvarkMigrator.new(v1_hash: record, collection_id_map: id_map).run
 ```
 
-### OpenGeoMetadata
+### Downloading metadata from OpenGeoMetadata
 
 #### Clone OpenGeoMetadata repositories locally
 
@@ -124,6 +138,13 @@ To index into Solr, GeoCombine requires a Solr instance that is running the
 $ bundle exec rake geocombine:index
 ```
 
+By default, GeoCombine will index only records using the Aardvark metadata format. If you instead want to index records using an older format (e.g. because your GeoBlacklight instance is version 3 or older), you can set the `SCHEMA_VERSION` environment variable:
+
+```sh
+# Only index schema version 1.0 records
+$ SCHEMA_VERSION=1.0 bundle exec rake geocombine:index
+```
+
 Indexes the `geoblacklight.json` files in cloned repositories to a Solr index running at http://127.0.0.1:8983/solr
 
 ##### Custom Solr location