💡 Add source documentation from recent conversations.

There have been some conversations in the last weeks which explained
several parts of the code, so add it to the source code documentation.
Also some other small source code documentation improvements.

include/plugin.php

@@ -47,7 +47,10 @@ function uninstall_plugin($plugin) {
 }
 
 /**
- * @brief installs an addon.
+ * @brief Installs an addon.
+ *
+ * This function is called once to install the addon (either from the cli or via
+ * the web admin). This will also call load_plugin() once.
  *
  * @param string $plugin name of the addon
  * @return bool
@@ -188,7 +191,9 @@ function visible_plugin_list() {
 
 
 /**
- * @brief registers a hook.
+ * @brief Registers a hook.
+ *
+ * @see ::Zotlabs::Extend::Hook::register()
  *
  * @param string $hook the name of the hook
  * @param string $file the name of the file that hooks into
@@ -219,6 +224,8 @@ function register_hook($hook, $file, $function, $priority = 0) {
 /**
  * @brief unregisters a hook.
  *
+ * @see ::Zotlabs::Extend::Hook::unregister
+ *
  * @param string $hook the name of the hook
  * @param string $file the name of the file that hooks into
  * @param string $function the name of the function that the hook called