Move types from dependencies to dev-dependencies

Closes GH-45.
Closes GH-52.

Reviewed-by: Christian Murphy <christian.murphy.42@gmail.com>

package.json

@@ -32,15 +32,15 @@
     "lib"
   ],
   "dependencies": {
-    "@types/unist": "^2.0.0",
-    "@types/vfile": "^3.0.0",
     "bail": "^1.0.0",
     "extend": "^3.0.0",
     "is-plain-obj": "^2.0.0",
     "trough": "^1.0.0",
     "vfile": "^4.0.0"
   },
   "devDependencies": {
+    "@types/unist": "^2.0.0",
+    "@types/vfile": "^3.0.0",
     "browserify": "^16.0.0",
     "dtslint": "^0.8.0",
     "nyc": "^14.0.0",

readme.md

@@ -71,6 +71,10 @@ and [opensource.guide][] ([GitHub][]).
 npm install unified
 ```
 
+This package comes with types.
+If you’re using TypeScript, make sure to also install [`@types/unist`][ts-unist]
+and [`@types/vfile`][ts-vfile].
+
 ## Use
 
 ```js
@@ -1107,6 +1111,10 @@ work on [`ware`][ware], as it was a huge initial inspiration.
 
 [npm]: https://docs.npmjs.com/cli/install
 
+[ts-unist]: https://www.npmjs.com/package/@types/unist
+
+[ts-vfile]: https://www.npmjs.com/package/@types/vfile
+
 [site]: https://unified.js.org
 
 [medium]: https://medium.com/unifiedjs