rename main folder to overview

To be consistent with the naming.

sidebars.js

@@ -4,28 +4,28 @@
 
 const sidebars = {
   main: [
-    "main/introduction",
-    "main/history",
-    "main/motivation-and-goals",
-    "main/why-waku",
-    "main/who-is-using-waku",
-    "main/implementations",
-    "main/how-does-it-work",
+    "overview/introduction",
+    "overview/history",
+    "overview/motivation-and-goals",
+    "overview/why-waku",
+    "overview/who-is-using-waku",
+    "overview/implementations",
+    "overview/how-does-it-work",
     {
       type: "category",
       label: "Concepts",
       collapsed: false,
       collapsible: true,
       items: [
-        "main/concepts/different-protocols",
-        "main/concepts/protocols-explained",
-        "main/concepts/protocols-overview-by-example",
-        "main/concepts/discovery-and-bootstrap",
-        "main/concepts/transports-in-waku",
-        "main/concepts/content-topics",
-        "main/concepts/security-features",
-        "main/concepts/research-in-progress",
-        "main/concepts/waku-vs-libp2p",
+        "overview/concepts/different-protocols",
+        "overview/concepts/protocols-explained",
+        "overview/concepts/protocols-overview-by-example",
+        "overview/concepts/discovery-and-bootstrap",
+        "overview/concepts/transports-in-waku",
+        "overview/concepts/content-topics",
+        "overview/concepts/security-features",
+        "overview/concepts/research-in-progress",
+        "overview/concepts/waku-vs-libp2p",
       ],
     },
   ],