fixed spelling mistake

Author: Sam

doc/index.md

@@ -7,7 +7,7 @@ Npgsql has an Entity Framework 6 provider. You can use it by installing the
 [EntityFramework6.Npgsql](https://www.nuget.org/packages/EntityFramework6.Npgsql/) nuget.
 
 ## Basic Usage ##
-Create an inheritor if DbConfiguration in the same assembly as your entity framework DbContext. Ensure that you configure provider services, a provider factory, a default connection factory as shown below:
+Create an inheritor of DbConfiguration in the same assembly as your entity framework DbContext. Ensure that you configure provider services, a provider factory, a default connection factory as shown below:
 
 ```
 class NpgSqlConfiguration : DbConfiguration