Added brief readmes for all plugins. (#2184)

platform/persistence/couch/README.md

@@ -1,2 +1,8 @@
-This bundle implements a connection to an external CouchDB persistence 
-store in Open MCT.
+# Couch DB Persistence Plugin
+An adapter for using CouchDB for persistence of user-created objects. The plugin installation function takes the URL 
+for the CouchDB database as a parameter.
+
+## Installation
+```js
+openmct.install(openmct.plugins.CouchDB('http://localhost:5984/openmct'))
+```

platform/persistence/elastic/README.md

@@ -1,2 +1,8 @@
-This bundle implements a connection to an external ElasticSearch persistence 
-store in Open MCT.
+# Elasticsearch Persistence Provider
+An adapter for using Elastic for persistence of user-created objects. The installation function takes the URL for an 
+Elasticsearch server as a parameter.
+
+## Installation
+```js
+openmct.install(openmct.plugins.Elasticsearch('http://localhost:9200'))
+```

platform/persistence/local/README.md

@@ -0,0 +1,9 @@
+# Local Storage Plugin
+Provides persistence of user-created objects in browser Local Storage. Objects persisted in this way will only be 
+available from the browser and machine on which they were persisted. For shared persistence, consider the 
+[Elasticsearch](../elastic/) and [CouchDB](../couch/) persistence plugins.
+
+## Installation
+```js
+openmct.install(openmct.plugins.LocalStorage());
+```