ccitt: add security considerations to documentation

Change-Id: Iea941fb87cf3aa5983dbb44ab836e08e6a6a6964
Reviewed-on: https://go-review.googlesource.com/c/image/+/855281
Reviewed-by: Nicholas Husin <husin@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Nicholas Husin <nsh@golang.org>

ccitt/reader.go

diff --git a/ccitt/reader.go b/ccitt/reader.go
index 340de05..333a2c1 100644
--- a/ccitt/reader.go
+++ b/ccitt/reader.go
@@ -5,6 +5,13 @@
 //go:generate go run gen.go
 
 // Package ccitt implements a CCITT (fax) image decoder.
+//
+// # Security Considerations
+//
+// This package is not hardened against malicious inputs.
+// Crashes, excessive CPU or memory consumption, or similar misbehavior
+// caused by malicious or corrupt inputs will be handled as ordinary bugs,
+// not vulnerabilities.
 package ccitt
 
 import (