add types-specific tsconfig template

Author: lobsterkatie

tsconfig-templates/README.md

@@ -1,5 +1,5 @@
 # `tsconfig` Templates
 
-Every package should get its own copy of these four files. Package-specific options should go in `tsconfig.json` and
-test-specific options in `tsconfig.test.json`. The `cjs` and `esm` files shouldn't need to be modified, and only exist
-because tsconfigs don't support multiple inheritence.
+Every package should get its own copy of these five files. Package-specific options should go in `tsconfig.json` and
+test-specific options in `tsconfig.test.json`. The `cjs`, `esm`, and `types` files shouldn't need to be modified, and
+only exist because tsconfigs don't support multiple inheritence.

tsconfig-templates/tsconfig.types.json

@@ -0,0 +1,10 @@
+{
+  "extends": "./tsconfig.json",
+
+  "compilerOptions": {
+    "declaration": true,
+    "declarationMap": true,
+    "emitDeclarationOnly": true,
+    "outDir": "build/types"
+  }
+}