Updated Postgresql-hstore (markdown)

Postgresql-hstore.md

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 # Postgres Hstore Extension
+
+## Notes
+
+* All values stored a strings
+* Access is done like hashes `something[:fun]`
+
+### Requirements
+
+* These columns need to be indexed and can be done so in two ways:
+ * GIN: indexes are three types faster to search, but they take more time to index. They also take more disk space. Use it when you have more than 100K unique terms.
+ * GiST: indexes are slower than GIN indexes, but they’re faster to update. Use it when you have up to 100K unique terms
+* When using Rails you can just use the `add_index` syntax
+ * ex: `add_index :users, :preferences, using: :gin`