Enhance documentation for Instance and Connection.

include/connection.hpp

@@ -68,6 +68,9 @@ struct event_type
 /*!
  *  @brief  Represents a connection to an instance. Used for requests.
  *
+ *  Do not make 2 requests with the same Connection at the same time. You can
+ *  create as many Connection%s as you want from one Instance.
+ *
  *  @since  0.1.0
  *
  *  @headerfile connection.hpp mastodonpp/connection.hpp

include/instance.hpp

@@ -38,6 +38,10 @@ using std::vector;
 /*!
  *  @brief  Holds the access data of an instance.
  *
+ *  Instance%s are needed to initialize Connection%s. All properties you set
+ *  here (with set_proxy(), set_useragent() and so on) are copied to every
+ *  Connection you initialize afterwards.
+ *
  *  @since  0.1.0
  *
  *  @headerfile instance.hpp mastodonpp/instance.hpp