Improve documentation of non-numeric entity ID's support

Some suggested minor changes - thanks for coming back to this - appreciate it?

1. +++ b/dynamic_entity_reference.install
   @@ -11,6 +11,23 @@ use Drupal\Core\Entity\Sql\SqlEntityStorageInterface;
   + * This is an incredible mess because
   

   incredible mess » immensely complicated

2. +++ b/dynamic_entity_reference.install
   @@ -11,6 +11,23 @@ use Drupal\Core\Entity\Sql\SqlEntityStorageInterface;
   + * \Drupal\Core\Entity\Sql\SqlContentEntityStorageSchema::saveFieldSchemaData(0
   

   0 » ) ?

3. +++ b/dynamic_entity_reference.install
   @@ -11,6 +11,23 @@ use Drupal\Core\Entity\Sql\SqlEntityStorageInterface;
   + * is protected so the field storage schema need to be saved into the key-value
   

   need » needs

4. +++ b/dynamic_entity_reference.install
   @@ -11,6 +11,23 @@ use Drupal\Core\Entity\Sql\SqlEntityStorageInterface;
   + * yet another key-value storage which also needs to manually kept up-to-date.
   

   needs to » needs to be

5. +++ b/src/EventSubscriber/FieldStorageSubscriber.php
   @@ -69,6 +69,13 @@ class FieldStorageSubscriber implements EventSubscriberInterface {
   +    // When enabling a module implementing providing an entity type,
   

   implementing or providing but not both?

Very quick review during boarding:

+ * This is an immensely complicated because

minus an

- * Returns an appropriate plpgsql function name.
+ * Returns an appropriate pgsql function name.

plpgsql. That's a word and that's correct. https://www.postgresql.org/docs/8.3/static/plpgsql.html

Let's do this, I guess.