chore(env): comment describing relative path

Author: thekaveman

.env.sample

@@ -1,2 +1,7 @@
 FLASK_APP=eligibility_server/app.py
+
+# this sample uses an odd relative path because the value is
+# used by code under the eligibility_server directory
+# and thus the config folder is one level up
+
 ELIGIBILITY_SERVER_SETTINGS=../config/sample.py