update help section with session API docs

app/views/help/api.html.haml

@@ -13,6 +13,8 @@
     %a{href: "#snippets"} Snippets
   %li
     %a{href: "#users"} Users
+  %li
+    %a{href: "#session"} Session
   %li
     %a{href: "#issues"} Issues
   %li
@@ -58,6 +60,16 @@
 
 %br
 
+.file_holder#session
+  .file_title
+    %i.icon-file
+    Session
+  .file_content.wiki
+    = preserve do
+      = markdown File.read(Rails.root.join("doc", "api", "session.md"))
+
+%br
+
 .file_holder#issues
   .file_title
     %i.icon-file