Update README with some decriptions, features and roadmap

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

README.md

@@ -4,6 +4,12 @@
 
 Small utility to control Ceph cluster configuration just like any other declarative configuration
 
+## Main features
+
+- Easy-to-use healthcheck which may contain checks against status & configuration and indicate some some not trivial issues
+- Declarative configuration support which is apply only if needed
+- Diff configuration: check what the difference between currently running configuration and desired or migrated from other cluster
+
 ## Usage
 
 ```shell
@@ -41,6 +47,22 @@ version
 
 ```
 
+## How it works
+
+Cephctl uses native Ceph CLIs to work with cluster configuration so it's required to have
+Ceph binaries w/ configured `ceph.conf`. Alternatively it's possible to adjust `ceph` binary
+path to access ceph in container and/or remote machine.
+
+## Roadmap
+
+- [X] Apply declarative configuration for `ceph config`
+- [X] Dump cluster configuration to CephConfig specification
+- [X] Diff configuration against running configuration for `ceph config`
+- [X] Perform healthcheck based on current cluster status
+- [ ] Add healthchecks based on current cluster configuration
+- [ ] Apply/Dump declarative configuration for `ceph osd set-*` stuff
+- [ ] Apply/Dump declarative configuration for Ceph Object Gateway (rgw)
+
 ## Compatibility
 
 All of the changes are tested against Ceph 18.2 (Reef), previous versions are