hash/maphash: mention that hash values do not persist in package docs

Updates #36878
Fixes #37040

Change-Id: Ib0bd21481e5d9c3b3966c116966ecfe071243a24
Reviewed-on: https://go-review.googlesource.com/c/go/+/218297
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

doc/go1.14.html

@@ -616,6 +616,10 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
     <p>
       The hash functions are collision-resistant but not cryptographically secure.
     </p>
+    <p>
+      The hash value of a given byte sequence is consistent within a
+      single process, but will be different in different processes.
+    </p>
   </dd>
 </dl><!-- hash/maphash -->
 

src/hash/maphash/maphash.go

@@ -9,6 +9,9 @@
 //
 // The hash functions are collision-resistant but not cryptographically secure.
 // (See crypto/sha256 and crypto/sha512 for cryptographic use.)
+//
+// The hash value of a given byte sequence is consistent within a
+// single process, but will be different in different processes.
 package maphash
 
 import "unsafe"