Clean sample.env (#4666)

sample.env

+### SECRET KEY BASE
+# Verifies the integrity of all secrets created in the application
+# Can be generated by running 'docker run --rm --entrypoint /bin/sh bigbluebutton/greenlight:v3 -c "bundle exec rails secret"'
+SECRET_KEY_BASE=
+
+### BIGBLUEBUTTON CREDENTIALS
+# Set these if you are running GreenLight on a single BigBlueButton server.
+# You can retrieve these by running the following command on your BigBlueButton server:
+#   bbb-conf --secret
+BIGBLUEBUTTON_ENDPOINT=
+BIGBLUEBUTTON_SECRET=
+
 ### POSTGRES DATABASE URL
 # Must be in the format postgres://username:password@host:port/dbname
 #   E.g. postgres://postgres:password@postgres:5432/greenlight-v3-production
@@ -8,13 +20,30 @@ DATABASE_URL=
 #   E.g. redis://redis:6379
 REDIS_URL=
 
-### The endpoint and secret for your BigBlueButton server.
-# Set these if you are running GreenLight on a single BigBlueButton server.
-# You can retrieve these by running the following command on your BigBlueButton server:
+### SMTP CONFIGURATION
+# Emails are required for the basic features of Greenlight to function.
+# Please refer to your SMTP provider to get the values for the variables below
+SMTP_SENDER_EMAIL=
+SMTP_SENDER_NAME=
+SMTP_SERVER=smtp.gmail.com
+SMTP_PORT=465
+SMTP_DOMAIN=gmail.com
+SMTP_USERNAME=
+SMTP_PASSWORD=
+SMTP_AUTH=login
+SMTP_STARTTLS_AUTO=false
+SMTP_STARTTLS=false
+SMTP_TLS=true
+SMTP_SSL_VERIFY=true
+
+### OPTIONAL ENV VARS
+
+### EXTERNAL AUTHENTICATION METHODS
 #
-#   bbb-conf --secret
-#BIGBLUEBUTTON_ENDPOINT=
-#BIGBLUEBUTTON_SECRET=
+#OPENID_CONNECT_CLIENT_ID=
+#OPENID_CONNECT_CLIENT_SECRET=
+#OPENID_CONNECT_ISSUER=
+#OPENID_CONNECT_REDIRECT=
 
 # To enable hCaptcha on the user sign up and sign in, define these 2 keys
 #HCAPTCHA_SITE_KEY=
@@ -28,35 +57,7 @@ REDIS_URL=
 #S3_BUCKET=
 #S3_ENDPOINT=
 
-### GL3 secret key base.
-# openssl rand -hex 64
-SECRET_KEY_BASE=
-
-#PORT=
-#RAILS_ENV=
-#RAILS_SERVE_STATIC_FILES=
-
 # Define the default locale language code (i.e. 'en' for English) from the fallowing list:
 #  [en, ar, fr, es]
 #DEFAULT_LOCALE=en
 
-# SMTP configuration:
-#SMTP_SENDER_EMAIL=
-#SMTP_SENDER_NAME=
-#SMTP_SERVER=smtp.gmail.com
-#SMTP_PORT=465
-#SMTP_DOMAIN=gmail.com
-#SMTP_USERNAME=
-#SMTP_PASSWORD=
-#SMTP_AUTH=login
-#SMTP_STARTTLS_AUTO=false
-#SMTP_STARTTLS=false
-#SMTP_TLS=true
-#SMTP_SSL_VERIFY=true
-
-# OpenID configuration:
-#OPENID_CONNECT_CLIENT_ID=
-#OPENID_CONNECT_CLIENT_SECRET=
-#OPENID_CONNECT_ISSUER=
-#OPENID_CONNECT_REDIRECT=
-