update readme

weed/filer/arangodb/readme.md

@@ -27,3 +27,22 @@ omitempty means extra space is not used.
 
 i test with
 `docker run -p 8529:8529 -e ARANGO_ROOT_PASSWORD=test arangodb/arangodb:3.9.0`
+
+
+## todo
+
+implement native TTL
+
+
+## thoughts
+
+should there be one collection per bucket? would make deleting a bucket instant as compared to fast
+
+
+## comparison
+
+arangodb uses rocksdb in the background, so i am assuming things run in log time
+
+single document retreval might run in constant time
+
+i am not sure how the prefix query scales compared to the recursive calls that some other stores do for folder deletion