Add release notes for v1

[marlo-longley]

Important to let community know what's been changing! @dinahhandel

[jcoyne]

This should include:

• https://github.com/projectblacklight/arclight/blob/aabfad7b7d9b2a568964dc0f50112c1b454bacdf/lib/generators/arclight/install_generator.rb#L80-L91
• https://github.com/sul-dlss/nta-arclight/pull/62
• $breadcrumb-divider: quote(">"); in the scss before including blacklight
• Add *_is field to the solr schema. See https://github.com/projectblacklight/arclight/issues/1175
• Downloads of EAD XML and finding aid PDFs are now only rendering for collections. Previously there was the capability to have the download for any component. It was determined that this feature was not used as developed. See https://github.com/projectblacklight/arclight/pull/1257
• Rename configuration properties to not have _tab_. See https://github.com/projectblacklight/arclight/pull/1261
• Add configuration if you want to see the online icon in the catalog controller https://github.com/projectblacklight/arclight/pull/1275
• Add index breadcrumb configuration to CatalogController (https://github.com/projectblacklight/arclight/pull/1290)
• If you used collection_ssim, names_ssim, has_online_content_ssim, repository_ssim to create or manipulated paths or search_state, update them to there new values https://github.com/projectblacklight/arclight/pull/1359 You may want to wholly use the BlacklightConfiguration from CatalogController

[marlo-longley]

Ability to configure date normalizer for indexing (#1344)