Add docs and tests

packages/cache/README.md

@@ -6,8 +6,36 @@
 
 #### Restore Cache
 
+Restores a cache based on `key` and `restoreKeys` to the `paths` provided. Function returns the cache key for cache hit and returns undefined if cache not found. 
+
+```js
+const cache = require('@actions/cache');
+const paths = [
+    'node_modules',
+    'packages/*/node_modules/'
+]
+const key = 'npm-foobar-d5ea0750'
+const restoreKeys = [
+    'npm-foobar-',
+    'npm-'
+]
+const cacheKey = await cache.restoreCache(paths, key, restoreKeys)
+```
+
 #### Save Cache
 
+Saves a cache containing the files in `paths` using the `key` provided. Function returns the cache id if the cache was save succesfully.
+
+```js
+const cache = require('@actions/cache');
+const paths = [
+    'node_modules',
+    'packages/*/node_modules/'
+]
+const key = 'npm-foobar-d5ea0750'
+const cacheId = await cache.saveCache(paths, key)
+```
+
 ## Additional Documentation
 
 See ["Caching dependencies to speed up workflows"](https://help.github.com/github/automating-your-workflow-with-github-actions/caching-dependencies-to-speed-up-workflows).