Land rapid7#19715, Update README.md

Author: cgranleese-r7

db/README.md

@@ -1,2 +1,10 @@
-Contains `modules_metadata_base.json` which contains information about all modules within Metasploit, as well as
-`schema.rb` which describes current state of the database schema maintained by Rails ActiveRecord.
+This directory contains the following files:
+
+- `modules_metadata_base.json`, which contains information about all modules within Metasploit.
+- `schema.rb`, which is auto-generated from the current state of the database schema maintained by Rails ActiveRecord.
+  This file is auto-generated from the current state of the database.
+
+`schema.rb` is the source Rails uses to define your schema when running `bin/rails db:schema:load`. When creating a new 
+database, `bin/rails db:schema:load` tends to be faster and is potentially less error-prone than running all of your 
+migrations from scratch. Old migrations may fail to apply correctly if those migrations use external dependencies or 
+application code. We _strongly_ recommend that you check this file into your version control system.