Updates to build instructions example

Author: mayankchetan

share/docker/README.md

@@ -8,7 +8,7 @@ and `openfast` added. The image built by this `Dockerfile` can be customised at
 
 ## Image registry
 Production images of OpenFAST for the `linux/amd64` platform are available on the 
-[NREL docker hub](https://hub.docker.com/r/nrel/openfast).
+[NREL docker hub](https://hub.docker.com/r/nrel/openfast) and OpenFAST's [GitHub Container Registry](https://github.com/OpenFAST/openfast/pkgs/container/openfast).
 
 ## Build arguments
 Provide any of the following build arguments to customise the image at build time. 
@@ -25,7 +25,7 @@ For example, to build OpenFAST v3.5.3 for the `linux/amd64` platform and set `CM
 ```shell
 # Run from the root of this repository.
 git checkout v3.5.3
-docker build -f share/docker/Dockerfile -t openfast:3.5.3 --platform=linux/amd64 --build-arg=CMAKE_OPTIONS='-DBUILD_TESTING=ON' .
+docker build -f share/docker/Dockerfile -t openfast:3.5.3 --platform=linux/amd64 --build-arg=CMAKE_OPTIONS='-DCMAKE_BUILD_TYPE=RELEASE' .
 ```
 
 **NOTE:** This version of the `Dockerfile` is only available in v3.5.3 and up of this repository. To build earlier