add readme for segcache crate (#116)

* add readme for segcache module

* bump revision

src/storage/segcache/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "segcache"
-version = "0.1.0"
+version = "0.1.1"
 description = "Pelikan segment-structured cache"
 authors = ["Brian Martin <brian@pelikan.io>"]
 

src/storage/segcache/README.md

@@ -0,0 +1,20 @@
+Segcache is a cache storage engine that delivers high memory efficiency, high
+throughput, and excellent scalability for web cache workloads.
+
+The design is optimized for workloads that access predominantly small objects
+and use TTL (time-to-live). These workloads, which represent most of what social
+media websites, as well as a good portion of web workloads in general, have
+historically paid a significant memory overhead due to their small object sizes
+and transient nature. In Twitter's case, which was where this design was
+originally developed in collaboration with Carnegie Mellon University, the cache
+memory footprint was reduced by as much as 60%. This was achieved while
+maintaining comparable or better throughput to best-in-kind alternatives, such
+as the slab memory allocator in [Memcached](https://memcached.org) and its
+cousin in [Twemcache](https://github.com/twitter/twemcache). Segcache also
+offers much better (write) scalability compared to Memcached.
+
+The design was first published as a conference paper at NSDI’21, titled “Pelikan
+Segcache: a memory-efficient and scalable in-memory key-value cache for small
+objects”. It received NSDI Community Award, and the code used in the paper is
+merged into Pelikan codebase as of April 2021. A more detailed description can
+be found in the form of a [blog post](https://pelikan.io/2021/segcache.html).