Describe some basics in README (#2)

Signed-off-by: Igor Shishkin <me@teran.dev>

README.md

@@ -1,3 +1,39 @@
 # archived
 
-Cloud native service so store versioned data in space-efficient manner
+Cloud native service to store versioned data in space-efficient manner
+
+## How it works
+
+archived is inspired by `rsync --link-dest` which allowed to store package
+mirrors without duplicating data for decades. And now archived makes this
+approach unbound from local file systems by using modern era storage services
+under the hood like S3.
+
+To do so archived relies on two storages: metadata and CAS.
+
+Metadata is a some kind of database to store all of the things:
+
+* containers - some kind of directories
+* versions - immutable version of the data in container
+* objects - named data BLOBs with some additional metadata
+
+Good example of metadata storage is a PostgreSQL database.
+
+CAS storage is a BLOB storage which stores the data behind objects.
+CAS is actually an acronym means Content Addressed Storage which describes
+how exactly it operates: stores BLOBs under content aware unique key (SHA256
+is used by default).
+
+Good example of CAS storage is S3.
+
+This approach allows to reduce raw data usage by linking duplicates instead
+if storing copies.
+
+## archived components
+
+archived is built with microservice architecture containing the following
+components:
+
+* access - HTTP server to allow data listing and fetching
+* manage - gRPC API to manage containers, versions and objects
+* CLI - CLI application to interact with manage component