added a quick short README

Author: suhasjs

diskann-record/README.md

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+# DiskANN Record
+
+This crate provides a small framework for persisting structured Rust values as a 
+manifest (can be serialized to JSON) plus a set of side-car binary artifacts, and 
+reloading them later. It is can be used by `diskann` providers and indexes to 
+implement durable, consistent and backward-compatible checkpoints.
+
+Types describe how they map to a versioned record by implementing the `save::Save` and
+`load::Load` traits; the `save_fields!` and `load_fields!` macros handle the
+field-by-field plumbing for plain structs. Every record carries a `Version` so loaders
+can detect schema changes and either upgrade or fall back through a probing chain.
+
+The goal is to allow crates like `diskann` to checkpoint their state without depending on
+a particular serialization backend. This crate has minimal dependencies by design.