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/documentation_best_practices.md b/docs/documentation_best_practices.md
index 328a98f..4e4df45 100644
--- a/docs/documentation_best_practices.md
+++ b/docs/documentation_best_practices.md
@@ -97,7 +97,7 @@
     design. However, once the code is implemented, design docs should serve as
     archives of these decisions, not as half-correct docs (they are often
     misused). See
-    [Implementation state](#implementation_state_determines_document_location)
+    [Implementation state](#Implementation-state-determines-document-repository)
     below.
 
 ## Implementation state determines document repository