bcachefs: add runtime replication examples (#13486)

Co-authored-by: spageektti <git@spageektti.cc>

pages/linux/bcachefs.md

@@ -23,6 +23,14 @@
 
 `bcachefs fs usage --human-readable {{path/to/mountpoint}}`
 
+- Set replicas after formatting and mounting:
+
+`sudo bcachefs set-fs-option --metadata_replicas={{2}} --data_replicas={{2}} {{path/to/partition}}`
+
+- Force `bcachefs` to ensure all files are replicated:
+
+`sudo bcachefs data rereplicate {{path/to/mountpoint}}`
+
 - Display help:
 
 `bcachefs`