doc: update README

Author: ymgyt

README.md

@@ -6,15 +6,45 @@
 
 Syndicationd is a TUI feed viewer, based on [feed-rs](https://github.com/feed-rs/feed-rs) and [ratatui](https://github.com/ratatui-org/ratatui).
 
-## Development
 
-```sh
-# Setup local environment
-nix develop
+## Features
 
-# Run check
-just check
-```
+* Subscribe feeds(RSS1, RSS2, Atom,...) and browse latest entries 
+* Open the entry in a browser
+
+
+## Install
+
+### Nix
+
+`nix run github:ymgyt/syndicationd`
+
+### Cargo
+
+`cargo install synd-term --locked`
+
+
+## Usage
+
+### Log file
+
+The log file path is based on [`ProjectDirs::data_dir()`](https://docs.rs/directories/latest/directories/struct.ProjectDirs.html#method.data_dir).  
+Please refer to the `--log` flag in `synd --help` for the default output destination.  
+
+You can modify the [log directives](https://docs.rs/tracing-subscriber/latest/tracing_subscriber/filter/struct.EnvFilter.html#directives) using the environment variable `SYND_LOG`. (for example, `SYND_LOG=synd=debug`)
+
+### Theme
+
+The theme can be changed using the `--theme` flag. Please refer to the help for the values that can be specified.
+
+### Backend api
+
+By default, use `https://syndicationd.ymgyt.io` as the backend api([hosted on my home Raspberry Pi](https://github.com/ymgyt/mynix/blob/main/homeserver/modules/syndicationd/default.nix)).  
+To change the endpoint, specify the `--endpoint` flag
+
+### Clear cache and logs
+
+Authentication credentials are cached. to remove them, execute `synd clear`.
 
 ## License