The system context tracks OS level information, such as the process ID and hostname.
Note: This context is automatically added when each Timber.Logentry is created. There is no need to add it yourself.
Timber.Logentry
m() :: %{hostname: String.t | nil, pid: String.t | nil}
t() :: %Timber.Contexts.SystemContext{hostname: String.t | nil, pid: String.t | nil}