Merge pull request ceph#60256 from joscollin/wip-doc-update-key-idea

doc: update Key Idea in cephfs-mirroring.rst

Reviewed-by: Venky Shankar <[email protected]>
Reviewed-by: Anthony D'Atri <[email protected]>
Reviewed-by: Zac Dover <[email protected]>

Author: zdover23

doc/dev/cephfs-mirroring.rst

@@ -17,12 +17,10 @@ Key Idea
 --------
 
 For a given snapshot pair in a directory, `cephfs-mirror` daemon will rely on
-readdir diff to identify changes in a directory tree. The diffs are applied to
+`CephFS Snapdiff Feature` to identify changes in a directory tree. The diffs are applied to
 directory in the remote file system thereby only synchronizing files that have
 changed between two snapshots.
 
-This feature is tracked here: https://tracker.ceph.com/issues/47034.
-
 Currently, snapshot data is synchronized by bulk copying to the remote
 filesystem.
 
@@ -407,3 +405,5 @@ Feature Status
 --------------
 
 `cephfs-mirror` daemon is built by default (follows `WITH_CEPHFS` CMake rule).
+
+.. _CephFS Snapdiff Feature: https://croit.io/blog/cephfs-snapdiff-feature