Add configuration

README.md

@@ -55,6 +55,39 @@ gh-threads --repo owner/repository \
   --endpoint https://github.example.com/api/graphql
 ```
 
+## Configuration
+
+The optional TOML configuration is loaded from
+`$GH_THREADS_CONFIG`, `$XDG_CONFIG_HOME/gh-threads/config.toml`, or the
+operating system's user configuration directory at `gh-threads/config.toml`.
+On Linux this is normally `~/.config/gh-threads/config.toml`. On macOS,
+`~/Library/Application Support/gh-threads/config.toml` is preferred, with
+`~/.config/gh-threads/config.toml` automatically used as a fallback when it
+exists.
+
+```toml
+theme = "dark"                 # "dark" or "light"
+refresh_interval = "10s"
+repository = ""               # optional owner/repository default
+show_all = false              # requires repository
+limit = 50
+endpoint = "https://api.github.com/graphql"
+
+[display]
+fold_resolved = true
+thread_list_width_percent = 33 # 20-60
+
+[paths]
+scroll = false
+scroll_interval = "350ms"      # minimum 50ms
+```
+
+Command-line flags override the configuration. `GH_REPO` overrides the
+configured repository when `--repo` is not provided. The corresponding flags
+include `--config`, `--theme`, `--poll`, `--fold-resolved`,
+`--thread-list-width`, `--path-scroll`, and `--path-scroll-interval`. Boolean
+settings can be disabled explicitly, for example `--path-scroll=false`.
+
 ## Keys
 
 | Key | Action |