[calls] manager: Add section documentation

[Evangelos Ribeiro Tzaras <devrtz src gnome org>]

commit d7ba7927d71298b4e82542e75006b67258079667
Author: Evangelos Ribeiro Tzaras <devrtz fortysixandtwo eu>
Date:   Sun Feb 6 09:56:31 2022 +0100

    manager: Add section documentation

 src/calls-manager.c | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/src/calls-manager.c b/src/calls-manager.c
index a39175b4..f0fc9f87 100644
--- a/src/calls-manager.c
+++ b/src/calls-manager.c
@@ -42,6 +42,17 @@
 #include <glib/gi18n.h>
 #include <libpeas/peas.h>
 
+/**
+ * SECTION:manager
+ * @short_description: Central management object
+ * @Title: CallsManager
+ *
+ * #CallsManager is a singleton that manages lists of loaded #CallsProvider,
+ * #CallsOrigin and #CallsCall objects. It keeps track of which #CallsOrigin
+ * supports which protocol. It also checks which #CallsCall are ongoing and
+ * emits signals for the UI and other parts of the application to act on.
+ */
+
 static const char * const protocols[] = {
   "tel",
   "sip",