Add Linux docker for debugging info to README

This commit adds a short paragraph explaining how to create a quick and
easy Docker for testing your changes in a Linux environment when you
don't have an easy access to a Linux device.

Author: cristeahub

README.md

@@ -64,6 +64,28 @@ $ SWIFT_DRIVER_ENABLE_INTEGRATION_TESTS=1 \
   swift test --parallel
 ```
 
+#### Preparing a Linux docker for debug
+
+When developing on macOS without quick access to a Linux machine, using a Linux Docker is often helpful when debugging.
+
+To get a docker up and running to the following:
+- Install Docker for Mac.
+- Get the newest swift docker image `docker pull swift`.
+- Run the following command to start a docker
+```
+$ docker run -v /path/to/swift-driver:/home/swift-driver \
+  --cap-add=SYS_PTRACE --security-opt seccomp=unconfined \
+  --security-opt apparmor=unconfined -it swift:latest bash
+```
+- Install dependencies by running
+```
+$ apt-get update
+$ apt-get install libsqlite3-dev
+$ apt-get install libncurses-dev
+```
+- You can now go to `/home/swift-driver` and run `swift test --parallel` to run your tests.
+
+
 ### Rebuilding `Options.swift`
 
 `Options.swift`, which contains the complete set of options that can be parsed by the driver, is automatically generated from the [option tables in the Swift compiler](https://github.com/apple/swift/tree/master/include/swift/Option). If you need to regenerate `Options.swift`, you will need to [build the Swift compiler](https://github.com/apple/swift#building-swift) and then build `makeOptions` program with a `-I` that allows the generated `Options.inc` to