Merge pull request #3801 from github/secrets-naming-info

Add note about GITHUB_ tokens in codespaces secrets documentation

content/github/developing-online-with-codespaces/managing-encrypted-secrets-for-codespaces.md

@@ -12,6 +12,7 @@ versions:
 
 {% endnote %}
 
+
 ### About encrypted secrets for {% data variables.product.prodname_codespaces %}
 
 You can add encrypted secrets to your user account that you want to use in your codespaces. For example, you may want to store and access the following sensitive information as encrypted secrets.
@@ -24,6 +25,12 @@ You can choose which repositories should have access to each secret. Then, you c
 
 ### Adding a secret
 
+{% note %}
+
+**Note:** Tokens starting with GITHUB_ are reserved
+
+{% endnote %}
+
 {% data reusables.user_settings.access_settings %}
 {% data reusables.user_settings.codespaces-tab %}
 1. To the right of "Codespaces secrets", click **New secret**.