Add doc lins to unicode packages

core/unicode/doc.odin

@@ -0,0 +1,2 @@
+// package unicode provides data and procedures to test properties of Unicode code points
+package unicode

core/unicode/utf16/utf16.odin

@@ -1,3 +1,4 @@
+// package utf16 implements procedures and constants to support text-encoding in the UTF-16 character encoding
 package utf16
 
 import "core:unicode/utf8"

core/unicode/utf8/utf8.odin

@@ -1,3 +1,4 @@
+// package utf8 implements procedures and constants to support text-encoding in the UTF-8 character encoding
 package utf8
 
 RUNE_ERROR :: '\ufffd'