update README to inform about new plumbing comman

Author: Byron

README.md

@@ -38,6 +38,8 @@ become available.
     * **pack-index**
       * [x] [index from data](https://asciinema.org/a/352941) - create an index file by streaming a pack file as done during clone
           * [ ] support for thin packs (as needed for fetch/pull)
+    * **commit-graph**
+      * [ ] **verify** - assure that a commit-graph is consistent
     * [remote-ref-list](https://asciinema.org/a/359320)
       * [x] list all (or given) references from a remote at the given URL
 

tasks.md

@@ -27,7 +27,7 @@
 
 ### Commit-Graph
 
-* [ ] A plumbing command to extract some value from the current implementation, maybe statistics, or verification
+* [x] A plumbing command to extract some value from the current implementation, maybe statistics, or verification
 * [ ] Application of the command above in a stress test
 
 * **Questions**