readme, some fixes

src/main.rs

@@ -82,7 +82,13 @@ async fn main() -> anyhow::Result<()> {
     .await?;
 
     if let Some(handle) = args.value_of("auth") {
+        let handle = handle.to_lowercase();
         let acct = handle.trim_start_matches('@');
+
+        if store.group_exists(acct).await {
+            anyhow::bail!("Group already exists in config!");
+        }
+
         if let Some(server) = acct_to_server(acct) {
             let g = store
                 .auth_new_group(NewGroupOptions {