Update the schema usage instructions.

I believe package resolution for `"$schema"` is *supposed* to work in VS Code, but it definitely doesn't. So it has to be a relative path.

Author: lgarron

README.md

@@ -42,9 +42,10 @@ Options:
 Requires `rsync` to be installed. Reads target URLs from a field in `package.json` in the current folder:
 
 {
+  "$schema": "./node_modules/@cubing/deploy/config-schema.package.json",
   "@cubing/deploy": {
     "https://experiments.cubing.net/test/deploy": {}
-  },
+  }
 }
 
 This example will be deployed from the following folder:

src/lib/args.ts

@@ -17,9 +17,10 @@ Options:
 Requires \`rsync\` to be installed. Reads target URLs from a field in \`package.json\` in the current folder:
 
 {
+  "$schema": "./node_modules/@cubing/deploy/config-schema.package.json",
   "@cubing/deploy": {
     "https://experiments.cubing.net/test/deploy": {}
-  },
+  }
 }
 
 This example will be deployed from the following folder: