Add docs on how to get a preview of markdown pages.

site/dev/tools/markdown.md

Index: site/dev/tools/markdown.md
diff --git a/site/dev/tools/markdown.md b/site/dev/tools/markdown.md
index 66feb9460e65cf285e3063237a74ed81848855da..c7a73243363631cbecd10a4567eb3a132c26fefc 100644
--- a/site/dev/tools/markdown.md
+++ b/site/dev/tools/markdown.md
@@ -7,6 +7,12 @@ Any file you put under `/site/` that has the extension `.md` will be processed
 as MarkDown. All other files will be served directly. For example, images
 can be added and they will be served correctly and referenced from within MarkDown files.
 
+When preparing for a code review of site docs you can get a preview of how the
+page will render by visiting the skia.org site and add a query parameter `cl`
+with the value of the Reitveld issue id:
+
+    https://skia.org?cl=REITVELD_ISSUE_NUMBER

[tfarina, 2015/01/28 16:43:42]

Doing just that does not work.

For example, navigating to https://skia.org/?cl=878593002, you are directed to
the Overview page.

But if you navigate to https://skia.org/dev/tools/markdown?cl=878593002 then it
will render the preview of this change.

https://codereview.chromium.org/883003004

+
 Some Example MarkDown
 ---------------------