Document option gc.writeCommitGraph Change-Id: Ic02d5abce18250b30f2c3f3741892d8cda251001

diff --git a/Documentation/config-options.md b/Documentation/config-options.md
index 84c4f5a..ff223ab 100644
--- a/Documentation/config-options.md
+++ b/Documentation/config-options.md

@@ -77,6 +77,7 @@
 | `gc.pruneExpire` | `2.weeks.ago` | &#x2705; | Grace period after which unreachable objects will be pruned. |
 | `gc.prunePackExpire` | `1.hour.ago` |  &#x20DE; | Grace period after which packfiles only containing unreachable objects will be pruned. |
 | `gc.writeChangedPaths` | `false`| &#x20DE; | Whether bloom filter should be written to commit-graph during a gc operation. |
+| `gc.writeCommitGraph`| `false` | &#x20DE; | If true, then gc will rewrite the commit-graph file when jgit gc is run. |
 
 ## __http__ options