Add docs for platform specific type conversions

README.md

@@ -3,7 +3,7 @@
 [![GoDoc](https://godoc.org/github.com/graymeta/stow?status.svg)](https://godoc.org/github.com/graymeta/stow)
 [![Go Report Card](https://goreportcard.com/badge/github.com/graymeta/stow)](https://goreportcard.com/report/github.com/graymeta/stow)
 
-Cloud storage abstraction package for Go. 
+Cloud storage abstraction package for Go.
 
 * Version: 0.1.0
 * Project status: Stable. Approaching v1 release
@@ -27,7 +27,7 @@ Stow provides implementations for storage services, blob stores, cloud storage e
 
 ## Concepts
 
-The concepts of Stow are modelled around the most popular object storage services, and are made up of three main objects:
+The concepts of Stow are modeled around the most popular object storage services, and are made up of three main objects:
 
 * `Location` - a place where many `Container` objects are stored
 * `Container` - a named group of `Item` objects
@@ -84,6 +84,7 @@ import (
 The underscore indicates that you do not intend to use the package in your code. Importing it is enough, as the implementation packages register themselves with Stow during initialization.
 
 * For more information about using Stow, see the [Best practices documentation](BestPractices.md).
+* Some implementation packages provide ways to access the underlying connection details for use-cases where more control over a specific service is needed. See the implementation package documentation for details.
 
 ### Connecting to locations
 

google/README.md

@@ -6,6 +6,42 @@ Container = Bucket
 
 Item = File
 
+## How to access underlying service types
+
+Use a type conversion to extract the underlying `Location`, `Container`, or `Item` implementations. Then use the Google-specific getters to access the internal Google Cloud Storage `Service`, `Bucket`, and `Object` values.
+
+```go
+import (
+  "log"
+  "github.com/graymeta/stow"
+  stowgs "github.com/graymeta/stow/google"
+)
+
+stowLoc, err := stow.Dial(stowgs.Kind, stow.ConfigMap{
+	stowgs.ConfigJSON:      "<json config>",
+	stowgs.ConfigProjectId: "<project id>",
+})
+if err != nil {
+  log.Fatal(err)
+}
+
+stowBucket, err = stowLoc.Container("mybucket")
+if err != nil {
+  log.Fatal(err)
+}
+
+if gsBucket, ok := stowBucket.(*stowgs.Bucket); ok {
+  if gsLoc, ok := stowLoc.(*stowgs.Location); ok {
+
+    googleService := gsLoc.Service()
+    googleBucket := gsBucket.Bucket()
+
+    // < Send platform-specific commands here >
+
+  }
+}
+```
+
 ---
 
 Configuration... You need to create a project in google, and then create a service account in google tied to that project. You will need to download a `.json` file with the configuration for the service account. To run the test suite, the service account will need edit privileges inside the project.