Add explanation.md

simple_web/explanation.md

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+# An explanation for the code in this dir
+
+```
+AsyncWebServer server(80);
+```
+Start the Web Server on port 80
+
+```
+WiFi.begin(ssid, password);
+  if (WiFi.waitForConnectResult() != WL_CONNECTED) {
+    Serial.printf("WiFi Failed!\n");
+    return;
+}
+```
+Start the WIFI with `WiFi.begin(ssid, password);` and wait for connection
+
+```
+server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){
+        request->send(200, "text/html", "<a href=\"/on\">Turn the LED ON</a><a href=\"/off\">Turn the LED OFF</a>");
+    });
+```
+`server.on` Defines an Endpoint for a request (e.g /index.html) 
+
+`request->send(200, "text/html", "<button onclick=\"fetch('http://192.168.178.198/on')\">Turn LED ON</button> <button onclick=\"fetch('http://192.168.178.198/off')\">Turn LED OFF</button>");` on Request answer with 200 in the format text/html with this string
+
+```
+server.on("/on", HTTP_GET, [](AsyncWebServerRequest *request){
+        request->send(200, "text/plain", "Was there ever anything here?");
+        digitalWrite(LED_BUILTIN, HIGH);
+    });
+```
+This is for when the user clicks on the ON button and fetches the /on url it turns the LED on!