add 0 to tadoku level with th the meaning of all levels

rsshub/spiders/tadoku/books.py

@@ -12,6 +12,7 @@ def parse(post):
     return item
 
 def ctx(category=''):
+    category = category  if category != '0' else ''
     url = f"{domain}/japanese/book-search?level={category}"
     tree = fetch(url,headers=DEFAULT_HEADERS)
     posts = tree.css('.col-6.col-sm-4.col-md-3.col-lg-2.bl-wrap-small')

rsshub/templates/main/feeds.html

@@ -243,7 +243,7 @@
         <h6 class="text-muted">图书 <a href="https://github.com/hillerliao" target="_blank" class="badge badge-secondary">by hillerliao</a></h6>
         <p class="card-text">举例：<a href="https://pyrsshub.vercel.app/tadoku/books/l0" target="_blank">https://pyrsshub.vercel.app/tadoku/books/l0</a></p>
         <p class="card-text">路由：<code>/tadoku/books/:category</code></p>
-        <p class="card-text">参数：category [必填，难度等级，l0、l1、l2、l3、l4、l5 ]</p>
+        <p class="card-text">参数：category [必填，难度等级，l0、l1、l2、l3、l4、l5、0。0为不指定 ]</p>
     </div>
 </div>
 <br>