Add detail to README following Michele Titolo's suggestions.

Author: timburks

README.md

@@ -7,7 +7,7 @@ and code generator.
 
 It is intended for use with Apple's 
 [swift-protobuf](https://github.com/apple/swift-protobuf)
-support for Protocol Buffers. Both projects contain 
+support for Protocol Buffers. Both projects contain
 code generation plugins for `protoc`, Google's 
 Protocol Buffer compiler, and both contain libraries
 of supporting code that is needed to build and run
@@ -29,26 +29,92 @@ systems. Please see [DOCKER.md](DOCKER.md) and
 
 ## gRPC dependencies are vendored
 
-Swift gRPC now includes vendored copies of the gRPC core 
+Swift gRPC includes vendored copies of the gRPC core
 library and **BoringSSL**, an OpenSSL fork that is used by
 the gRPC Core. These are built automatically in Swift Package
 Manager builds.
 
-## Building with Xcode
+## Usage
+
+The recommended way to use Swift gRPC is to first define an API using the
+[Protocol Buffer](https://developers.google.com/protocol-buffers/)
+language and then use the
+[Protocol Buffer Compiler](https://github.com/google/protobuf)
+and the [Swift Protobuf](https://github.com/apple/swift-protobuf)
+and [gRPC-Swift](https://github.com/grpc/grpc-swift) plugins to
+generate the necessary support code.
+
+### Getting the dependencies
+
+Binary releases of `protoc`, the Protocol Buffer Compiler, are
+available on [GitHub](https://github.com/google/protobuf/releases).
+
+To build the plugins, run `make` in the [Plugins](Plugins) directory.
+This uses the Swift Package Manager to build both of the necessary
+plugins: `protoc-gen-swift`, which generates Protocol Buffer support code
+and `protoc-gen-swiftgrpc`, which generates gRPC interface code.
+
+### Using the plugins
+
+To use the plugins, `protoc` and both plugins should be in your
+search path. Invoke them with commands like the following:
+
+    protoc <your proto files> \
+        --swift_out=. \
+        --swift_opt=Visibility=Public \
+        --plugin=<path to protoc-gen-swift>`
+
+    protoc <your proto files> \
+        --swiftgrpc_out=.
+
+By convention the `--swift_out` option invokes the `protoc-gen-swift`
+plugin and `--swiftgrpc_out` invokes `protoc-gen-swiftgrpc`.
+
+The `--swift_opt` flag passes an option to `protoc-gen-swift` that
+makes message classes public, which is necessary to use them with
+gRPC. The `--plugin` option is only needed by older versions of
+`protoc` that are unable to find the plugin binaries when options
+are specified.
+
+### Building your project
+
+Most `grpc-swift` development is done with the Swift Package Manager.
+For usage in Xcode projects, we rely on the `swift package generate-xcodeproj`
+command to generate an Xcode project for the `grpc-swift` core libraries.
 
 The top-level Makefile uses the Swift Package Manager to
 generate an Xcode project for the SwiftGRPC package:
 
     $ make
 
-Then open `SwiftGRPC.xcodeproj` in Xcode. Due to present
+This will create `SwiftGRPC.xcodeproj`, which you should
+add to your project, along with setting build dependencies
+on **BoringSSL**, **CgRPC**, and **gRPC**. Due to present
 limitations in Package Manager configuration, the libz
 dependency is not included in the generated Xcode project. If
 you get build errors about missing symbols such as
 `_deflate`, `_deflateEnd`, etc., you can fix them by adding
 `libz.tbd` to the **Link Binary With Libraries** build step
 of the **CgRPC** target.
 
+Please also note that your project will need to include the
+**SwiftProtobuf.xcodeproj** from
+[Swift Protobuf](https://github.com/apple/swift-protobuf) and
+the source files that you generated with `protoc` and the plugins.
+
+Please see [Echo](Examples/Echo) for a working Xcode-based
+example and file issues if you find any problems.
+
+### Low-level gRPC
+
+While the recommended way to use gRPC is with Protocol Buffers
+and generated code, at its core gRPC is a powerful HTTP/2-based
+communication system that can support arbitrary payloads. As such,
+each gRPC library includes low-level interfaces that can be used
+to directly build API clients and servers with no generated code.
+For an example of this in Swift, please see the
+[Simple](Examples/Simple) example.
+
 ## Having build problems?
 
 grpc-swift depends on Swift, Xcode, and swift-proto. We are currently