Add logging statements to the shim

Right now then code in the shim fails it looks like the error is inside of the buildpack itself. For example this error:

```
[builder] -----> Detecting rails configuration
[builder] exit status 127
[builder] ERROR: failed to build: exit status 3
ERROR: failed to build: executing lifecycle. This may be the result of using an untrusted builder: failed with status code: 51
```

Appears to indicate that the problem happened in `bin/compile` when in fact that was successful and the real problem didn't happen until `bin/release`. By logging our intentions to the output it makes it clearer to understand where failures are happening if/when they do happen.

bin/build

@@ -122,8 +122,12 @@ cache_dir="${layers_dir}/shim"
 mkdir -p "${cache_dir}"
 echo "cache = true" >"${layers_dir}/shim.toml"
 
+echo "-----> Running bin/compile"
+
 "${target_dir}/bin/compile" "${app_dir}" "${cache_dir}" "${platform_dir}/env"
 
+echo "-----> Setting up profile.d scripts"
+
 # copy profile.d scripts into a layer so they will be sourced
 if [[ -d .profile.d ]]; then
 	profile_dir="${layers_dir}/profile"
@@ -149,11 +153,15 @@ EOF
 	echo "launch = true" >"${profile_dir}.toml"
 fi
 
+echo "-----> Setting up exports"
+
 if [[ -f "${target_dir}/export" ]]; then
 	echo "build = true" >>"${profile_dir}.toml"
 	mkdir -p "${profile_dir}/env.build/"
 	"${bp_dir}/bin/exports" "${target_dir}/export" "${platform_dir}" "${profile_dir}/env.build/"
 fi
 
+echo "-----> Running bin/release"
+
 # run bin/release, read Procfile, and generate launch.toml
 "${bp_dir}/bin/release" "${target_dir}" "${layers_dir}" "${platform_dir}" "${app_dir}"