docs: document blob upload CLI flags for zodb-convert

Add changelog entries and update README Options section with
--background-blobs, --deferred-blobs, and --upload-blobs flags.

Author: jensens

CHANGES.md

@@ -1,5 +1,16 @@
 # Changelog
 
+## Unreleased
+
+- Add `--background-blobs` flag: upload blobs to S3 in a background thread pool,
+  decoupled from PG writes. Significantly faster for large migrations where S3
+  latency is the bottleneck. Only effective with parallel workers (`-w`).
+- Add `--deferred-blobs PATH` flag: write blob upload tasks to a manifest file
+  instead of uploading to S3 during migration. Process the manifest later with
+  `--upload-blobs`.
+- Add `--upload-blobs MANIFEST` flag: upload deferred blobs from a manifest file
+  (created by `--deferred-blobs`) with parallel workers and retry logic.
+
 ## 1.0.0b9
 
 - Support `--incremental -w N` together. Previously, `--incremental`

README.md

@@ -103,6 +103,13 @@ Where `convert.conf` contains only the destination storage section.
 
 - `--dry-run` — show what would be copied without making changes
 - `--incremental` — resume from the last transaction in the destination
+- `-w N` / `--workers N` — number of parallel writer threads (default: 1)
+- `--background-blobs` — upload blobs to S3 in a background thread pool,
+  decoupled from PG writes (faster for large migrations)
+- `--deferred-blobs PATH` — write blob upload tasks to a manifest file
+  instead of uploading during migration
+- `--upload-blobs MANIFEST` — upload deferred blobs from a manifest file
+  (created by `--deferred-blobs`)
 - `-v` / `--verbose` — increase verbosity (`-v` for INFO, `-vv` for DEBUG)
 
 ## Source Code and Contributions