Use ReST admonition syntax for note

Co-authored-by: Felix Fontein <felix@fontein.de>
Signed-off-by: Carlos Zubieta <1976312+ErraticMaker@users.noreply.github.com>

README.rst

@@ -669,8 +669,10 @@ of all new files. If your secrets are stored under a specific directory, like a
 ``git`` repository, you can create a ``.sops.yaml`` configuration file at the root
 directory to define which keys are used for which filename.
 
-Note: The file needs to be named ``.sops.yaml``. Other names (i.e. ``.sops.yml``) won't be automatically
-discovered by sops. You'll need to pass the ``--config .sops.yml`` option for it to be picked up.
+.. note::
+
+  The file needs to be named ``.sops.yaml``. Other names (i.e. ``.sops.yml``) won't be automatically
+  discovered by SOPS. You'll need to pass the ``--config .sops.yml`` option for it to be picked up.
 
 Let's take an example: