Remove old docker files and add doc for using docker (#749)

* Remove old docker files and add doc for using docker with dotnet-buildtools-prereqs

* Updates based on PR feedback

* Fixing up headers

* Added commit used for docker files

* Fix problem with table

* Add source-build commit in verified column.

* Fix column alignment

docker/README.md

@@ -0,0 +1,63 @@
+# Docker Images #
+
+The following docker images have been verified to successfully build the source-build repo by:
+
+1. Building source-build
+2. Building the resulting tarball
+3. Running smoke tests
+
+| OS | Image Name | Image Source | Verified Source-build Commit / Date |
+| :--- | :--- | :--- | :---: |
+| CentOS 7.1 | microsoft/dotnet-buildtools-prereqs:centos-7-b46d863-20180719033416 | [Dockerfile](https://github.com/dotnet/dotnet-buildtools-prereqs-docker/blob/b46d86339939ada16dfb8be30ebe62fbd51d3999/src/centos/7/Dockerfile) | [4f3eacd](https://github.com/dotnet/source-build/commit/4f3eacdd0551677444ab917d4e332653672e0bd5) / 2018.09.05 |
+| Fedora 28 | microsoft/dotnet-buildtools-prereqs:fedora-28-c103199-20180628122443 | [Dockerfile](https://github.com/dotnet/dotnet-buildtools-prereqs-docker/blob/c103199065cb74842c2983f0422ea4a1f0b0fe25/src/fedora/28/Dockerfile) | [4f3eacd](https://github.com/dotnet/source-build/commit/4f3eacdd0551677444ab917d4e332653672e0bd5) / 2018.09.05 |
+| Ubuntu 16.04 | microsoft/dotnet-buildtools-prereqs:ubuntu-16.04-c103199-20180628134544 |[Dockerfile](https://github.com/dotnet/dotnet-buildtools-prereqs-docker/blob/c103199065cb74842c2983f0422ea4a1f0b0fe25/src/ubuntu/16.04/Dockerfile) | [4f3eacd](https://github.com/dotnet/source-build/commit/4f3eacdd0551677444ab917d4e332653672e0bd5) / 2018.09.05 |
+
+## Building source-build with Docker ##
+
+### Running an interactive docker container ###
+```
+### Run a bash shell inside a docker container. All later steps run in the interactive shell.
+docker run -it --rm <imageName> /bin/bash
+
+### Clone source-build repo
+git clone https://github.com/dotnet/source-build
+cd source-build
+
+### Build source-build to create a tarball
+./build-source-tarball.sh ../tarball
+
+### Build the tarball
+cd ../tarball
+./build.sh
+
+### Run smoke tests
+./smoke-test.sh
+
+### Clean up the container when you're done working with the build results
+exit
+```
+
+### Running with a docker volume ###
+Running build commands in a docker container with a docker volume for a working directory.  A docker volume allows you to persist data across docker container instances.
+```
+### Create a volume on which to build source-build
+docker volume create source-build-volume 
+
+### Clone source-build repo
+docker run --rm --mount source=source-build-volume,target=/src -w /src <imageName> /bin/bash -c "git clone https://github.com/dotnet/source-build"
+
+### Build source-build to create a tarball
+docker run --rm --mount source=source-build-volume,target=/src -w /src/source-build <imageName> /bin/bash -c "./build-source-tarball.sh ../tarball"
+
+### Build the tarball
+docker run --rm --mount source=source-build-volume,target=/src -w /src/tarball <imageName> /bin/bash -c "./build.sh"
+
+### Run smoke tests
+docker run --rm --mount source=source-build-volume,target=/src -w /src/tarball <imageName> /bin/bash -c "./smoke-test.sh"
+
+### Run an interactive container with the docker volume
+docker run -it --rm --mount source-build-volume,target=/src -w /src <imageName> /bin/bash
+
+### Remove a volume when finished with it
+docker volume rm source-build-volume
+```