Specify where to add feature flag info on page

We tell the user to add info about enabling or disabling a feature
flag, but the only place we say "add it to the end of the file" is
in the code block itself. We should be clearer about where we expect
this subheading to be placed.

doc/development/documentation/feature_flags.md

@@ -52,7 +52,7 @@ Include details of the feature flag in the documentation:
   [by-project information](#features-enabled-by-project). Otherwise,
   do not say anything about it.
 - Say whether it's recommended for production use.
-- Document how to enable and disable it.
+- Document how to enable and disable it, preferably at the end of the file.
 - Add a warning to the user saying that the feature might be disabled.
 
 For example, for a feature disabled by default, disabled on GitLab.com, cannot
@@ -110,7 +110,7 @@ default:
   [by-project information](#features-enabled-by-project). Otherwise,
   do not say anything about it.
 - Say whether it's recommended for production use.
-- Document how to disable and enable it.
+- Document how to disable and enable it, preferably at the end of the file.
 - Add a warning to the user saying that the feature might be disabled.
 
 For example, for a feature initially deployed disabled by default, that became
@@ -169,7 +169,7 @@ For features enabled by default:
   [by-project information](#features-enabled-by-project). Otherwise,
   do not say anything about it.
 - Say whether it's recommended for production use.
-- Document how to disable and enable it.
+- Document how to disable and enable it, preferably at the end of the file.
 - Add a warning to the user saying that the feature might be disabled.
 
 For example, for a feature enabled by default, enabled on GitLab.com, that