add comments to release section of rebar.config template

priv/templates/relx_rebar.config

@@ -6,16 +6,28 @@
          [@@name@@,
           sasl]},
 
+        {mode, dev},
+
+        %% automatically picked up if the files
+        %% exist but can be set manually, which
+        %% is required if the names aren't exactly
+        %% sys.config and vm.args
         {sys_config, "./config/sys.config"},
-        {vm_args, "./config/vm.args"},
+        {vm_args, "./config/vm.args"}
 
-        {dev_mode, true},
-        {include_erts, false},
+        %% the .src form of the configuration files do
+        %% not require setting RELX_REPLACE_OS_VARS
+        %% {sys_config_src, "./config/sys.config.src"},
+        %% {vm_args_src, "./config/vm.args.src"}
+]}.
 
-        {extended_start_script, true}]
-}.
+{profiles, [{prod, [{relx,
+                     [%% prod is the default mode when prod
+                      %% profile is used, so does not have
+                      %% to be explicitly included like this
+                      {mode, prod}
 
-{profiles, [{prod, [{relx, [{dev_mode, false},
-                            {include_erts, true}]}]
-            }]
-}.
+                      %% use minimal mode to exclude ERTS
+                      %% {mode, minimal}
+                     ]
+            }]}]}.