Clear cache docs (#4667)

* add to changelog for PR #4430

* add —clearCache to docs

CHANGELOG.md

@@ -14,6 +14,7 @@
 * `[jest-util]` Fix `runOnlyPendingTimers` for `setTimeout` inside `setImmediate` ([#4608](https://github.com/facebook/jest/pull/4608))
 
 ### Features
+* `[jest-cli]` Add an option to clear the cache ([#4430](https://github.com/facebook/jest/pull/4430))
 * `[babel-plugin-jest-hoist]` Improve error message, that the second argument of `jest.mock` must be an inline function ([#4593](https://github.com/facebook/jest/pull/4593))
 * `[jest-snapshot]` [**BREAKING**] Concatenate name of test and snapshot ([#4460](https://github.com/facebook/jest/pull/4460))
 * `[jest-cli]` Add an option to fail if no tests are found ([#3672](https://github.com/facebook/jest/pull/3672))

docs/CLI.md

@@ -79,12 +79,16 @@ Alias: `-b`. Exit the test suite immediately upon the first failing test suite.
 
 Whether to use the cache. Defaults to true. Disable the cache using `--no-cache`. *Note: the cache should only be disabled if you are experiencing caching related problems. On average, disabling the cache makes Jest at least two times slower.*
 
-If you want to inspect or clear the cache, use `--showConfig` and look at the `cacheDirectory` value.
+If you want to inspect the cache, use `--showConfig` and look at the `cacheDirectory` value. If you need to clear the cache, use `--clearCache`.
 
 ### `--ci`
 
 When this option is provided, Jest will assume it is running in a CI environment. This changes the behavior when a new snapshot is encountered. Instead of the regular behavior of storing a new snapshot automatically, it will fail the test and require Jest to be run with `--updateSnapshot`.
 
+### `--clearCache` 
+##### available in Jest **21.3.0+**
+Deletes the Jest cache directory and then exits without running tests. Will delete `cacheDirectory` if the option is passed, or Jest's default cache directory. The default cache directory can be found by calling `jest --showConfig`. *Note: clearing the cache will reduce performance.*
+
 ### `--collectCoverageFrom=<glob>`
 
 Relative to the root directory, glob pattern matching the files that coverage info needs to be collected from.