public Builder addPlatform(String architecture, String os) {
      platforms.add(new Platform(architecture, os));
      return this;
    }
Adds a desired image platform (OS and architecture pair). If the base image reference is a
Docker manifest list or an OCI image index, an image builder may select the base image
matching the given platform. If the base image reference is an image manifest, an image
builder may ignore the given platform and use the platform of the base image or may decide to
raise on error.

<p>Note that a new build plan starts with "amd64/linux" as the default platform. If you want
to reset the default platform instead of adding a new one, use {@link #setPlatforms(Set)}.

@param architecture architecture (for example, {@code amd64}) to select a base image in case
    of a manifest list
@param os OS (for example, {@code linux}) to select a base image in case of a manifest list
@return this
jib-build-plan/src/main/java/com/google/cloud/tools/jib/api/buildplan/ContainerBuildPlan.java