Clarify config template comments (#8891)

changelog.d/8891.doc

+Clarify comments around template directories in `sample_config.yaml`.

docs/sample_config.yaml

@@ -1879,11 +1879,8 @@ sso:
     #  - https://my.custom.client/
 
     # Directory in which Synapse will try to find the template files below.
-    # If not set, default templates from within the Synapse package will be used.
-    #
-    # DO NOT UNCOMMENT THIS SETTING unless you want to customise the templates.
-    # If you *do* uncomment it, you will need to make sure that all the templates
-    # below are in the directory.
+    # If not set, or the files named below are not found within the template
+    # directory, default templates from within the Synapse package will be used.
     #
     # Synapse will look for the following templates in this directory:
     #
@@ -2113,9 +2110,8 @@ email:
   #validation_token_lifetime: 15m
 
   # Directory in which Synapse will try to find the template files below.
-  # If not set, default templates from within the Synapse package will be used.
-  #
-  # Do not uncomment this setting unless you want to customise the templates.
+  # If not set, or the files named below are not found within the template
+  # directory, default templates from within the Synapse package will be used.
   #
   # Synapse will look for the following templates in this directory:
   #

synapse/config/emailconfig.py

@@ -390,9 +390,8 @@ class EmailConfig(Config):
           #validation_token_lifetime: 15m
 
           # Directory in which Synapse will try to find the template files below.
-          # If not set, default templates from within the Synapse package will be used.
-          #
-          # Do not uncomment this setting unless you want to customise the templates.
+          # If not set, or the files named below are not found within the template
+          # directory, default templates from within the Synapse package will be used.
           #
           # Synapse will look for the following templates in this directory:
           #

synapse/config/sso.py

@@ -93,11 +93,8 @@ class SSOConfig(Config):
             #  - https://my.custom.client/
 
             # Directory in which Synapse will try to find the template files below.
-            # If not set, default templates from within the Synapse package will be used.
-            #
-            # DO NOT UNCOMMENT THIS SETTING unless you want to customise the templates.
-            # If you *do* uncomment it, you will need to make sure that all the templates
-            # below are in the directory.
+            # If not set, or the files named below are not found within the template
+            # directory, default templates from within the Synapse package will be used.
             #
             # Synapse will look for the following templates in this directory:
             #