Update README.md

Co-authored-by: Tommaso Pavese <tompave@users.noreply.github.com>

README.md

@@ -596,7 +596,7 @@ config :fun_with_flags, :persistence,
   repo: MyApp.Repo,
   ecto_table_name: "your_table_name", # optional, defaults to "fun_with_flags_toggles"
   ecto_primary_key_type: :binary_id # optional, defaults to :id
-  # For the primary key type, see also: https://hexdocs.pm/ecto/Ecto.Schema.html#module-schema-attributes
+  # For the primary key type, see also: https://hexdocs.pm/ecto/3.10.3/Ecto.Schema.html#module-schema-attributes
 ```
 
 It's also necessary to create the DB table that will hold the feature flag data. To do that, [create a new migration](https://hexdocs.pm/ecto_sql/Mix.Tasks.Ecto.Gen.Migration.html) in your project and copy the contents of [the provided migration file](https://github.com/tompave/fun_with_flags/blob/master/priv/ecto_repo/migrations/00000000000000_create_feature_flags_table.exs). Then [run the migration](https://hexdocs.pm/ecto_sql/Mix.Tasks.Ecto.Migrate.html).