limit formatOnSave option to JS/TS files, add docs re: prettier

.vscode/extensions.json

@@ -1,3 +0,0 @@
-{
-  "recommendations": ["eg2.tslint", "EditorConfig.EditorConfig", "esbenp.prettier-vscode"]
-}

.vscode/settings.json

@@ -1,6 +1,5 @@
 {
   "editor.renderWhitespace": "boundary",
-  "editor.formatOnSave": true,
   "files.encoding": "utf8",
   "files.trimTrailingWhitespace": true,
   "files.insertFinalNewline": true,
@@ -11,5 +10,14 @@
     "node_modules/**": true,
     "typings/**": true
   },
-  "typescript.tsdk": "./node_modules/typescript/lib"
+  "typescript.tsdk": "./node_modules/typescript/lib",
+  "[json]": {
+    "editor.formatOnSave": true
+  },
+  "[javascript]": {
+    "editor.formatOnSave": true
+  },
+  "[typescript]": {
+    "editor.formatOnSave": true
+  }
 }