rename plugin-search-indexer to plugin-search-backend-node

Signed-off-by: Eric Peterson <ericpeterson@spotify.com>

plugins/search-backend-node/README.md

@@ -0,0 +1,21 @@
+# search-backend-node
+
+This plugin is part of a suite of plugins that comprise the Backstage search
+platform, which is still very much under development. This plugin specifically
+is responsible for:
+
+- Allowing other backend plugins to register the fact that they have documents
+  that they'd like to be indexed by a search engine (known as `collators`)
+- Allowing other backend plugins to register the fact that they have metadata
+  that they'd like to augment existing documents in the search index with
+  (known as `decorators`)
+- A scheduler that, at configurable intervals, compiles documents to be indexed
+  and passes them to a search engine for indexing
+- Types for all of the above
+
+Documentation on how to develop and improve the search platform is currently
+centralized in the `search` plugin README.md.
+
+For a better overview of how the search platform is put together, check the
+[Backstage Search Architecture](https://backstage.io/docs/features/search/architecture)
+documentation.