Add Phriction to the main nav menu

Summary:
A few minor things:

  - Add Phriction to the homepage.
  - Link to remarkup reference on the edit screen.
  - Add a help tab with a super basic help document.

Test Plan: Cursory inspection.
Reviewed By: codeblock
Reviewers: hsb, codeblock, jungejason, tuomaspelkonen, aran
CC: aran, epriestley, codeblock
Differential Revision: 655

resources/sql/patches/062.phrictionmenu.sql

@@ -0,0 +1,9 @@
+/* Older versions incorrectly computed the depth for the root page. */
+UPDATE phabricator_phriction.phriction_document
+  SET depth = 0 where slug = '/';
+
+INSERT INTO phabricator_directory.directory_item
+  (name, description, href, categoryID, sequence, dateCreated, dateModified)
+VALUES
+  ("Phriction", "Write things down.", "/w/", 4, 1100,
+    UNIX_TIMESTAMP(), UNIX_TIMESTAMP());