Added support for multistage build cache

README.md

@@ -463,6 +463,37 @@ builder:
   context: ".."
 ```
 
+### Using multistage builder cache
+
+Docker multistage build cache can singlehandedly speed up your builds by a lot. Currently MRSK only supports using the GHA cache or the Registry cache:
+
+```yaml
+# Using GHA cache
+builder:
+  cache:
+    type: gha
+
+# Using Registry cache
+builder:
+  cache:
+    type: registry
+
+# Using Registry cache with different cache image
+builder:
+  cache:
+    type: registry
+    # default image name is <image>-build-cache
+    image: application-cache-image
+
+# Using Registry cache with additinonal cache-to options
+builder:
+  cache:
+    type: registry
+    options: mode=max,image-manifest=true,oci-mediatypes=true
+```
+
+For further insights into build cache optimization, check out documentation on Docker's official website: https://docs.docker.com/build/cache/.
+
 ### Using build secrets for new images
 
 Some images need a secret passed in during build time, like a GITHUB_TOKEN, to give access to private gem repositories. This can be done by having the secret in ENV, then referencing it in the builder configuration: