doc/go1.14: edit "Go command" section, adding note about go test -v s…

…treaming

Change-Id: Ie88fe441521d60a4ba54ebb418860d0f71073387
Reviewed-on: https://go-review.googlesource.com/c/go/+/216917
Reviewed-by: Bryan C. Mills <bcmills@google.com>

doc/go1.14.html

@@ -299,6 +299,14 @@ <h4 id="module-downloading">Module downloading</h4>
   graphic characters and spaces.
 </p>
 
+<h4 id="go.mod">Testing</h4>
+<!-- golang.org/issue/24929 -->
+
+<p>
+  <code>go test -v</code> now streams <code>t.Log</code> output as it happens,
+  rather than at the end of all tests.
+</p>
+
 <h2 id="runtime">Runtime</h2>
 
 <p><!-- CL 190098 -->