add postcss peer dep (#233)

Author: bluwy

package.json

@@ -43,11 +43,15 @@
     "typescript": "4.5.5"
   },
   "peerDependencies": {
-    "ts-node": ">=9.0.0"
+    "ts-node": ">=9.0.0",
+    "postcss": ">=8.0.9"
   },
   "peerDependenciesMeta": {
     "ts-node": {
       "optional": true
+    },
+    "postcss": {
+      "optional": true
     }
   },
   "keywords": [