Update the README

Author: thatbudakguy

README.md

@@ -32,18 +32,32 @@ $ gem install geo_combine
 ## 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
 ```
 
@@ -73,7 +87,7 @@ id_map = {
 GeoCombine::Migrators::V1AardvarkMigrator.new(v1_hash: record, collection_id_map: id_map).run
 ```
 
-### OpenGeoMetadata
+### Downloading metadata from OpenGeoMetadata
 
 #### Logging
 
@@ -144,6 +158,13 @@ You can also set a the Solr instance URL using `SOLR_URL`:
 $ SOLR_URL=http://www.example.com:1234/solr/collection 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
+```
+
 ### Harvesting and indexing documents from GeoBlacklight sites
 
 GeoCombine provides a Harvester class and rake task to harvest and index content from GeoBlacklight sites (or any site that follows the Blacklight API format). Given that the configurations can change from consumer to consumer and site to site, the class provides a relatively simple configuration API. This can be configured in an initializer, a wrapping rake task, or any other ruby context where the rake task our class would be invoked.