Documentation Revamp

Co-authored-by: jbdoumenjou <jb.doumenjou@gmail.com>

docs/content/middlewares/chain.md

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+# Chain
+
+When One Isn't Enougth
+{: .subtitle }
+
+![Chain](../assets/img/middleware/chain.png)
+
+The Chain middleware enables you to define reusable combinations of other pieces of middleware. 
+It makes reusing the same groups easier.
+
+## Configuration Example
+
+??? example "A Chain for WhiteList, BasicAuth, and HTTPS"
+    
+    ```toml
+    # ...    
+    [Routers]
+        [Routers.router1]
+            service = "service1"
+            middlewares = ["secured"]
+            rule = "Host: mydomain"
+    
+    [Middlewares]
+        [Middlewares.secured.Chain]
+            middlewares = ["https-only", "known-ips", "auth-users"]
+            
+        [Middlewares.auth-users.BasicAuth]
+            users = ["test:$apr1$H6uskkkW$IgXLP6ewTrSuBkTrqE8wj/"]
+        [Middlewares.https-only.SchemeRedirect]
+            scheme = "https"
+        [Middlewares.known-ips.ipWhiteList]
+            sourceRange = ["192.168.1.7", "x.x.x.x", "x.x.x.x"]
+    
+    [Services]
+      [Services.service1]
+        [Services.service1.LoadBalancer]
+          [[Services.service1.LoadBalancer.Servers]]
+            URL = "http://127.0.0.1:80"
+            Weight = 1
+    ```