feat: Add `book-open` icon

Closes #116

icons/book-open.svg

+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <path d="M2 3h6a4 4 0 0 1 4 4v14a3 3 0 0 0-3-3H2z" />
+  <path d="M22 3h-6a4 4 0 0 0-4 4v14a3 3 0 0 1 3-3h7z" />
+</svg>