Remove Docker section from README

They're no longer needed since CI runs tests automatically. The standard testing procedure for Rust crates should already be known and understood by anyone wishing to run them locally as well.

README.md

@@ -126,25 +126,6 @@ dumb_terminal = ["colored/no-color"]
 You can use have even finer control by using the
 `colored::control::set_override` method.
 
-## Build with Docker
-
-### Install Docker
-
-Use the install instructions located [here](https://docs.docker.com/v17.12/install/)
-
-### Build the Docker image
-
-```docker build -t colored_image .```
-
-### Build the library
-
-```docker run --rm -it -v "$PWD":/src -u `id -u`:`id -g` colored_image /bin/bash -c "cargo build"```
-
-### Test the library
-
-```docker run --rm -it -v "$PWD":/src -u `id -u`:`id -g` colored_image /bin/bash -c "cargo test"```
-
-
 ## Todo
 
 - **More tests ?**: We always welcome more tests! Please contribute!