C: pure_getline.c: add arguments docs

c-programming/pure_getline.c

@@ -9,6 +9,9 @@
 
 bool pure_getline(char** output) {
 	/*
+	 * arguments:
+	 * 	char** output: must be a pointer to an allocated array
+	 *
 	 * return value:
 	 * 	true: no errors
 	 * 	false: an error occurred, see errno