Readme: Fix shell installation (#1547)

Use the -s (silent) flag so curl does not pass metainformation like
downloadspeed etc to bash.

Co-authored-by: ChristopherHX <christopher.homberger@web.de>

README.md

@@ -115,7 +115,7 @@ nix run nixpkgs#act
 Run this command in your terminal:
 
 ```shell
-curl https://raw.githubusercontent.com/nektos/act/master/install.sh | sudo bash
+curl -s https://raw.githubusercontent.com/nektos/act/master/install.sh | sudo bash
 ```
 
 ### Manual download