Bug 5311: clarify configuration byte units (squid-cache#1979)

Author: kinkie

src/cf.data.pre

@@ -51,9 +51,10 @@ COMMENT_START
 
 	Units accepted by Squid are:
 		bytes - byte
-		KB - Kilobyte (1024 bytes)
-		MB - Megabyte
-		GB - Gigabyte
+		KB - Kilobyte (2^10, 1'024 bytes)
+		MB - Megabyte (2^20, 1'048'576 bytes)
+		GB - Gigabyte (2^30, 1'073'741'824 bytes)
+	Squid does not yet support KiB, MiB, and GiB unit names.
 
   Values with time units