update devcontainer template to open README.md instead of main.ptx, and to autoSave after delay

Author: oscarlevin

templates/devcontainer.json

@@ -18,9 +18,8 @@
   // "image": "pretextbook/pretext:latest",
   "features": {"ghcr.io/devcontainers/features/github-cli": {}},
 
-  // The pretext-full image above includes pretext, prefigure, and enough parts of latex and sagemath for most cases.  If there are errors with sage, you can install the full sagemath package through Conda by running ./.devcontainer/installSage.sh, or uncommenting that line and rebuilding the container.
+  // The pretext-full image above includes pretext, prefigure, and enough parts of latex and sagemath for most cases.  Here we install additional dependencies.
   "postCreateCommand": {
-    // "install sagemath": "bash ./.devcontainer/installSage.sh",
     "install pandoc": "bash ./.devcontainer/installPandoc.sh",
     "mark repo as safe": "git config --global --add safe.directory $(pwd)"
     },
@@ -57,18 +56,18 @@
     }
   },
 
-  
+
   // Configure tool-specific properties.
   "customizations": {
     "codespaces": {
-      "openFiles": ["source/main.ptx"]
+      "openFiles": ["README.md"]
     },
     "vscode": {
       "settings": {
         "editor.quickSuggestions": {
           "other": "off"
         },
-        "files.autoSave": "onFocusChange",
+        "files.autoSave": "afterDelay",
         "editor.snippetSuggestions": "bottom",
         "xml.validation.enabled": true,
         "redhat.telemetry.enabled": false,