Added the environment variable in the example file (#2213)

This PR is a followup to #2204 where the access policies are getting
restricted. This adds the configuration setting to the .env.example with
usage instructions and it's effects on the platform.

.env.example

@@ -137,6 +137,10 @@ SSO_LOGIN_BUTTON_TEXT="Single Sign-On"
 ENABLE_FILE_DOWNLOADS_OPTION=true
 COPY_FILES_TO_NEW_VERSION=true
 
+# Allowed Access Policies [Optional] - This is a list of access policies that can be assigned to a newly submitted project on the 'Project Access' page.
+# The environment variable is a stringified list of access policies separated by commas
+ALLOWED_ACCESS_POLICIES="OPEN,RESTRICTED,CREDENTIALED,CONTRIBUTOR_REVIEW"
+
 # Used for bucket creation
 GCP_DOMAIN=