Added gulp to common pages.

pages/common/gulp.md

@@ -0,0 +1,12 @@
+# gulp
+
+> JavaScript task runner and streaming build system.
+> Tasks are defined within gulpfile.js at the project root.
+
+- Run the default task:
+
+`gulp`
+
+- Run individual tasks:
+
+`gulp {{task}} {{othertask}}`