Add package line docs to c and libc

core/c/c.odin

@@ -1,3 +1,4 @@
+// package c just defines the basic types used by C programs
 package c
 
 import builtin "base:builtin"

core/c/libc/doc.odin

@@ -0,0 +1,2 @@
+// package libc declares the commonly used things in "libc" (C standard library)
+package libc