Some documentation improvements

src/settings.h

@@ -32,7 +32,7 @@
 
 #define PASSWORD_EVAL_MAX 512
 
-/* holds user setting values */
+/* Holds user setting values defined in the toxic config file. */
 struct user_settings {
     int autolog;           /* boolean */
     int alerts;            /* boolean */

src/toxic.c

@@ -101,6 +101,9 @@ struct Winthread Winthread;
 struct cqueue_thread cqueue_thread;
 struct av_thread av_thread;
 struct arg_opts arg_opts;
+
+// This struct is not thread safe. It should only ever be written to from the main thread
+// before any other thread that uses it is initialized.
 struct user_settings *user_settings = NULL;
 
 static struct user_password {

src/windows.h

@@ -98,6 +98,13 @@ typedef enum {
    Uncomment if necessary */
 /* #define URXVT_FIX */
 
+/*
+ * Used to control access to global variables via a mutex, as well as to handle signals.
+ * Any file, variable or data structure that is used by the UI/Window thread and any other thread
+ * must be guarded by `lock`.
+ *
+ * There should only ever be one instance of this struct.
+ */
 struct Winthread {
     pthread_t tid;
     pthread_mutex_t lock;