use new theme docsy (#15)

Signed-off-by: Di Xu <stephenhsu90@gmail.com>

Author: dixudx

.gitmodules

@@ -1,3 +1,3 @@
-[submodule "themes/zdoc"]
-	path = themes/zdoc
-	url = https://github.com/zzossig/hugo-theme-zdoc.git
+[submodule "themes/docsy"]
+	path = themes/docsy
+	url = https://github.com/google/docsy

assets/icons/logo.png

@@ -0,0 +1,14 @@
+/*
+
+Add styles or override variables from the theme here.
+
+*/
+
+$orange:  #fd7e14;
+
+$primary:   $orange;
+$secondary: #88B04B;
+
+$link-color: #FDAC53;
+
+$font-size-base: 1.4rem;