Merge branch 'kh/doc-commit-graph' into next

Ramifications of turning off commit-graph has been documented a bit
more clearly.

* kh/doc-commit-graph:
  doc: add caveat about turning off commit-graph

Documentation/git-commit-graph.adoc

@@ -146,6 +146,12 @@ $ git show-ref -s | git commit-graph write --stdin-commits
 $ git rev-parse HEAD | git commit-graph write --stdin-commits --append
 ------------------------------------------------
 
+CAVEATS
+-------
+
+The existence of replace objects or commit grafts turns off reading or
+writing to the commit-graph. See linkgit:git-replace[1].
+
 CONFIGURATION
 -------------
 

Documentation/git-replace.adoc

@@ -145,6 +145,13 @@ commit instead of the replaced commit.
 There may be other problems when using 'git rev-list' related to
 pending objects.
 
+CAVEATS
+-------
+
+The existence of replace objects or commit grafts turns off reading or
+writing to the commit-graph, which can cause performance issues. See
+linkgit:git-commit-graph[1].
+
 SEE ALSO
 --------
 linkgit:git-hash-object[1]