Note on the name of the configuration file

Making explicit that only files named `.sops.yaml` will be auto-discovered. And alternative names (like `.sops.yml`) need to be used with the `--config` flag.

Converted from getsops/sops@ca66e3c

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

Author: felixfontein

content/en/docs/_index.md

@@ -689,6 +689,9 @@ 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.
+
 Let\'s take an example:
 
 -   file named **something.dev.yaml** should use one set of KMS A, PGP