To get "dotnet ef" you have to install Entity Framework Core Tools
Reference
https://docs.microsoft.com/en-us/ef/core/cli/dotnet
Install:
$ dotnet tool install --global dotnet-ef
$ cat << \EOF >> ~/.zprofile
# Add .NET Core SDK tools
export PATH="$PATH:/Users/ramiscaray/.dotnet/tools"
EOF
# Make available to current session
$ zsh -l
$ dotnet add package Microsoft.EntityFrameworkCore.Design
$ dotnet ef
$ dotnet ef migrations add AddBookDatabase
$ dotnet ef database update