Adding 'Indexes' sub section.

README.md

@@ -232,6 +232,12 @@ sql: converting argument $1 type: uint64 values with high bit set are not suppor
 
 By sticking with an int64 in our Go code, we eliminate the risk of ever encountering this error.
 
+### Indexes
+
+If you are not familiar with the concept of indexes in SQL databases, the official PostgreSQL documentation provides a [good introduction](https://www.postgresql.org/docs/current/indexes-intro.html) and a summary of different [index types](https://www.postgresql.org/docs/current/indexes-types.html). I recommend reading these quickly to give you an overview before continuing.
+
+In our case, it makes sense to create [GIN indexes](https://www.postgresql.org/docs/current/textsearch-indexes.html) on both the **genres** field and the lexemes generated by **to_tsvector()**, both which are used in the **WHERE** clause of our SQL query.
+
 ## Additional Information
 
 ### How different Go Types are encoded