Change default Python location. Update build instructions. Add container build instructions

src/consts.rs

@@ -48,5 +48,5 @@ lazy_static! {
         .map_or(THEME_COLOR_FALLBACK, |inner| u32::from_str_radix(&inner, 16)
             .unwrap_or(THEME_COLOR_FALLBACK));
     pub static ref PYTHON_LOCATION: String =
-        env::var("PYTHON_LOCATION").unwrap_or_else(|_| "venv/bin/python3".to_string());
+        env::var("PYTHON_LOCATION").unwrap_or_else(|_| "/usr/bin/python3".to_string());
 }