Update README (#6)

* Update README

* Make description a one-liner

README.md

@@ -1,61 +1,75 @@
-# cache-artifacts
-A shortcut action to cache Julia artifacts.
+# julia-actions/cache Action
 
-Using this action is equivalent to including the following step in your workflows:
-
-```yaml
-- uses: actions/cache@v1
-  env:
-    cache-name: cache-artifacts
-  with:
-    path: ~/.julia/artifacts
-      key: ${{ runner.os }}-test-${{ env.cache-name }}-${{ hashFiles('**/Project.toml') }}
-      restore-keys: |
-        ${{ runner.os }}-test-${{ env.cache-name }}-
-```
+A shortcut action to cache Julia artifacts, packages and (optionally) registries to reduce GitHub Actions running time.
 
 ## Usage
 
-### Inputs
+An example workflow that uses this action might look like this:
 
 ```yaml
-- uses: julia-actions/cache-artifacts@v1
-  with:
-    # The cache name is used as part of the cache key.
-    # It is equivalent to the cache-name environment variable in the snippet above.
-    #
-    # Default: cache-artifacts
-    cache-name: ''
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: julia-actions/setup-julia@v1
+    - uses: julia-actions/cache@v1
+    - uses: julia-actions/julia-buildpkg@v1
+    - uses: julia-actions/julia-runtest@v1
 ```
 
+By default, this caches the files in `~/.julia/artifacts/` and `~/.julia/packages/`.
+To also cache `~/.julia/registries/`, use
+
+```yaml
+    - uses: julia-actions/cache@v1
+      with:
+        cache-registries: "true"
+```
+
+Note that caching the registries may actually slow down the workflow running time on Windows runners.
+That is why caching the registries is disabled by default.
+
+### Inputs
+
+- `cache-name` - Name used as part of the cache keys
+- `cache-artifacts` - Whether to cache `~/.julia/artifacts/`. Enabled by default.
+- `cache-packages` - Whether to cache `~/.julia/packages/`. Enabled by default.
+- `cache-registries` - Whether to cache `~/.julia/registries/`. Disabled by default.
+
 ### Outputs
 
-```yaml
-outputs:
-  # A boolean value to indicate an exact match was found for the primary key.
-  # Forwarded from actions/cache, check its documentation for more info.
-  cache-hit: ''
-```
+- `cache-hit` - A boolean value to indicate an exact match was found for the primary key. Returns \"\" when the key is new. Forwarded from actions/cache.
+
+## How it works
+
+This action is a wrapper around <https://github.com/actions/cache>.
+In summary, this action stores the files in the aforementioned paths in one compressed file when running for the first time.
+This cached file is then restored upon the second run.
+The benefit of this is that downloading one big file is more quick than downloading many different files from many different locations.
 
 ## Third Party Notice
 
 This action is built around [`actions/cache`](https://github.com/actions/cache/) and includes parts of that action. `actions/cache` has been released under the following licence:
 
-
 > The MIT License (MIT)
-> 
+>
 > Copyright (c) 2018 GitHub, Inc. and contributors
-> 
+>
 > Permission is hereby granted, free of charge, to any person obtaining a copy
 > of this software and associated documentation files (the "Software"), to deal
 > in the Software without restriction, including without limitation the rights
 > to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 > copies of the Software, and to permit persons to whom the Software is
 > furnished to do so, subject to the following conditions:
-> 
+>
 > The above copyright notice and this permission notice shall be included in
 > all copies or substantial portions of the Software.
-> 
+>
 > THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 > IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 > FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE