Fix comments for `ResolveCustom` methods from `AliasAPI`

sources/Aliases/AliasesAPI.uc

@@ -323,10 +323,9 @@ public final function Text ResolveEntity(
  *  Custom alias sources are any type of alias source that isn't built-in into
  *  Acedia. They can either be added manually by the admin through config file.
  *
- *      Lookup of alias can fail if either alias does not exist in entity alias
- *  source or entity alias source itself does not exist
- *  (due to either faulty configuration or incorrect definition).
- *      To determine if entity alias source exists you can check
+ *      Lookup of alias can fail if either alias does not exist in specified
+ *  alias source or that alias source itself does not exist.
+ *      To determine if specified alias source exists you can check
  *  `_.alias.GetCustomSource()` value.
  *
  *  @param  alias           Alias, for which method will attempt to