Add some more details about what net-export contains.

In particular, a user assumed it would only include information from
incognito (which is a pretty reasonable assumption) and chose to enable
byte logging. Seems like we should make clear that's not the case.

Bug: None
Change-Id: I699784b34af9d28c48679fdcd1abc730936908f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2232699
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775693}

components/net_log/resources/net_export.html

@@ -43,7 +43,9 @@
 
       <div class="section-container">
         Click the button to start logging future network activity to a file on
-        disk.
+        disk. The log includes details of network activity from all of Chrome,
+        including incognito and non-incognito tabs, visited URLs, and
+        information about the network configuration.
         <a href="https://dev.chromium.org/for-testers/providing-network-details"
            target="_blank">
         See the Chromium website for more detailed instructions.</a>