doc UPDATE added explanations to plugins

Author: lePici

src/plugins.h

@@ -38,19 +38,22 @@ extern "C" {
  * Furthermore, there are several internal plugins, implementing built-in data types and selected derived types and YANG
  * extensions. These internal plugins uses the same API and can be taken as examples for implementing user plugins. Internal
  * plugins are always loaded with the first created [context](@ref howtoContext) and unloaded with destroying the last one.
- * The external plugins are in the same phase loaded from the default directories specified at compile time via cmake
- * variables `PLUGINS_DIR` (where the `extensions` and `types` subdirectories are added for each plugin type) or separately
- * via `PLUGINS_DIR_EXTENSIONS` and `PLUGINS_DIR_TYPES` for each plugin type. The default directories can be replaced runtime
- * using environment variables `LIBYANG_TYPES_PLUGINS_DIR` and `LIBYANG_EXTENSIONS_PLUGINS_DIR`.
+ * The external plugins are in the same phase loaded as dynamic shared objects (shared libraries) from the default directories
+ * specified at compile time via cmake variables `PLUGINS_DIR` (where the `extensions` and `types` subdirectories are added
+ * for each plugin type) or separately via `PLUGINS_DIR_EXTENSIONS` and `PLUGINS_DIR_TYPES` for each plugin type. The default
+ * directories can be replaced runtime using environment variables `LIBYANG_TYPES_PLUGINS_DIR` and `LIBYANG_EXTENSIONS_PLUGINS_DIR`.
+ * There is also a separate function ::lyplg_add() to manually add a plugin (dynamic shared object) anytime later.
+ * Another option to manually add an external plugin is using the ::lyplg_add_extension_plugin() or ::lyplg_add_type_plugin()
+ * which is useful when loading a dynamic shared object is problematic. These functions allow for setting the necessary callbacks
+ * for the plugin at runtime.
  *
  * Order of the plugins determines their priority. libyang searches for the first match with the extension and type, so the
  * firstly loaded plugin for the specific item is used. Since the internal plugins are loaded always before the external
  * plugins, the internal plugins cannot be replaced.
  *
- * There is also a separate function ::lyplg_add() to add a plugin anytime later. Note, that such a plugin is being used
- * after it is added with the lowest priority among other already loaded plugins. Also note that since all the plugins are
- * unloaded with the destruction of the last context, creating a new context after that starts the standard plugins
- * initiation and the manually added plugins are not loaded automatically.
+ * Note, that manually added plugin via lyplg_add*() function is added with the lowest priority among other already loaded plugins.
+ * Also note that since all the plugins are unloaded with the destruction of the last context, creating a new context after that
+ * starts the standard plugins initiation and the manually added plugins are not loaded automatically.
  *
  * The following pages contain description of the API for creating user plugins.
  *