Add all VS Code extensions and simplify cloud dev environment docs

Co-authored-by: TechQuery <19969570+TechQuery@users.noreply.github.com>

Author: Copilot

.devcontainer/devcontainer.json

@@ -6,8 +6,13 @@
       "extensions": [
         "tboox.xmake-vscode",
         "ms-vscode.cpptools-extension-pack",
+        "yzhang.markdown-all-in-one",
         "redhat.vscode-yaml",
-        "GitHub.copilot"
+        "esbenp.prettier-vscode",
+        "eamodio.gitlens",
+        "github.vscode-pull-request-github",
+        "github.vscode-github-actions",
+        "github.copilot"
       ]
     }
   }

ReadMe.md

@@ -13,11 +13,6 @@ The simplest C/C++ project template for beginners.
 
 2.  Click the **[<kbd>Open in GitHub codespaces</kbd>][2] button** on the top of ReadMe file, then an **online VS Code development environment** will be started immediately
 
-3.  Run following command in VS Code terminal to install XMake:
-    ```bash
-    curl -fsSL https://xmake.io/shget.text | bash
-    ```
-
 ## Install minimal All-in-One Development Environment in your computer
 
 ### Windows