Add demo library (books from Feedbooks)

apps/readest-app/src/data/demo/library.en.json

@@ -0,0 +1,10 @@
+{
+  "library": [
+    "https://cdn.readest.com/books/a-room-of-one-s-own.epub",
+    "https://cdn.readest.com/books/hamlet.epub",
+    "https://cdn.readest.com/books/meditations.epub",
+    "https://cdn.readest.com/books/the-great-gatsby.epub",
+    "https://cdn.readest.com/books/the-scarlet-letter.epub",
+    "https://cdn.readest.com/books/this-side-of-paradise.epub"
+  ]
+}

apps/readest-app/src/data/demo/library.zh.json

@@ -0,0 +1,3 @@
+{
+  "library": ["https://cdn.readest.com/books/four-great-classics.epub"]
+}