notify user about which denv is being used

[tomeichlersmith]

Is your feature request related to a problem? Please describe.
Often, especially when juggling multiple denvs on a system, reminding the user which is being used can help avoid confusion.

Describe the solution you'd like
I'm thinking this can just be done by adding a _denv_info after the config is loaded. This will keep it quiet but allow for users to easily enable.

Describe alternatives you've considered
You can deduce the denv config that was run by running denv config print in the same directory where the issue is being observed; however, that separation could lead to confusion if any cd is done accidentally.

Additional context
LDMX-Software/ldmx-sw#1505

[tomeichlersmith]

diff --git a/denv b/denv
index 945533f..cb8694a 100755
--- a/denv
+++ b/denv
@@ -490,6 +490,7 @@ _denv_load_config() {
       return 1
     fi
   fi
+  _denv_info "using denv at ${denv_workspace}"
   # I am choosing to allow sourcing unknown code
   # shellcheck disable=SC1091
   . "${denv_workspace}/.denv/config"