Update web-platform-tests docs

These updates address a number of issues that have come up in the past
week since the 2-way process was launched. See:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/QIRcSgN9AK4/0JY58rBhCAAJ
https://groups.google.com/a/chromium.org/d/msg/platform-predictability/SBnz6Um7y2A/pDXVSOrpDwAJ

Drive-by: fix section links in other documentation.

BUG=657117
[email protected]

Review-Url: https://codereview.chromium.org/2695963002
Cr-Commit-Position: refs/heads/master@{#450696}
diff --git a/docs/using_a_linux_chroot.md b/docs/using_a_linux_chroot.md
index 96fadfd..da37cfe 100644
--- a/docs/using_a_linux_chroot.md
+++ b/docs/using_a_linux_chroot.md
@@ -80,7 +80,7 @@
 following conditions.
 
 1.  Make sure `DISPLAY` is set. See the
-    [Running X apps](#Running_X_apps) section above.
+    [Running X apps](#Running-X-apps) section above.
 1.  Install `xdg-utils`, which includes `xdg-open`, a utility for finding the
     right application to open a file or URL with.
 1.  Install [Chrome](https://www.google.com/intl/en/chrome/browser/).