Update render style of note boxes

doc/user/group/subgroups/index.md

 # Subgroups
 
-> **Notes:**
+NOTE: **Note:**
 > - [Introduced][ce-2772] in GitLab 9.0.
 > - Not available when using MySQL as external database (support removed in
 >   GitLab 9.3 [due to performance reasons][issue]).
@@ -79,7 +79,7 @@ structure.
 
 ## Creating a subgroup
 
-> **Notes:**
+NOTE: **Note:**
 > - You need to be an Owner of a group in order to be able to create
 >   a subgroup. For more information check the [permissions table][permissions].
 > - For a list of words that are not allowed to be used as group names see the
@@ -136,10 +136,10 @@ From the image above, we can deduct the following things:
 
 ### Overriding the ancestor group membership
 
->**Note:**
+NOTE: **Note:**
 You need to be an Owner of a group in order to be able to add members to it.
 
->**Note:**
+NOTE: **Note:**
 A user's permissions in a subgroup cannot be lower than in any of its ancestor groups.
 Therefore, you cannot reduce a user's permissions in a subgroup with respect to its ancestor groups.