doc/go1.16: note that package path elements beginning with '.' are disallowed

For #43985

Change-Id: I1a16f66800c5c648703f0a0d2ad75024525a710f
Reviewed-on: https://go-review.googlesource.com/c/go/+/291389
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

Author: Bryan C. Mills

doc/go1.16.html

@@ -174,10 +174,12 @@ <h4 id="modules">Modules</h4>
   non-reproducible builds.
 </p>
 
-<p><!-- golang.org/issue/43052 -->
-  The <code>go</code> command now disallows non-ASCII import paths in module
-  mode. Non-ASCII module paths have already been disallowed so this change
-  affects module subdirectory paths that contain non-ASCII characters.
+<p><!-- golang.org/issue/43052, golang.org/issue/43985 -->
+  In module mode, the <code>go</code> command now disallows import paths that
+  include non-ASCII characters or path elements with a leading dot character
+  (<code>.</code>). Module paths with these characters were already disallowed
+  (see <a href="/ref/mod#go-mod-file-ident">Module paths and versions</a>),
+  so this change affects only paths within module subdirectories.
 </p>
 
 <h4 id="embed">Embedding Files</h4>