doc/next: improve wording for proposal 67061

For #67061.
For #65614.

Change-Id: I0e324b02537e0d40c2092139d31941a1a85a0e69
Reviewed-on: https://go-review.googlesource.com/c/go/+/592196
Reviewed-by: Roland Shoemaker <roland@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@golang.org>

Author: dmitshur

doc/next/6-stdlib/99-minor/crypto/tls/66214.md

@@ -1,3 +1,3 @@
 3DES cipher suites were removed from the default list used when
-[Config.CipherSuites] is nil. The default can be reverted adding `tls3des=1` to
+[Config.CipherSuites] is nil. The default can be reverted by adding `tls3des=1` to
 the GODEBUG environment variable.

doc/next/6-stdlib/99-minor/crypto/tls/67061.md

@@ -1,2 +1,3 @@
-<!-- TODO: Improve the wording. Mention the tlskyber GODEBUG. -->
-X25519Kyber768Draft00 is now enabled by default when [Config.CurvePreferences] is not set.
+The experimental post-quantum key exchange mechanism X25519Kyber768Draft00
+is now enabled by default when [Config.CurvePreferences] is nil.
+The default can be reverted by adding `tlskyber=0` to the GODEBUG environment variable.