Add a test case for typer.enable_rich(<bool>)

Also, add a paragraph to the documentation.

docs/tutorial/printing.md

@@ -140,6 +140,11 @@ In general, **Typer** tends to be the entry point to your program, taking the fi
 
 The best results for your command line application would be achieved combining both **Typer** and **Rich**.
 
+### If you don't want to use Rich formated output
+
+In case you'd rather like to use the simple text ouput, but need **Rich** to be installed in your environment for any other reason, you can disable the use of **Rich** by **Typer** with the following call:`typer.enable_rich(False)`. This is a global switch affecting all instances of `typer.Typer()`.
+
+
 ## "Standard Output" and "Standard Error"
 
 The way printing works underneath is that the **operating system** (Linux, Windows, macOS) treats what we print as if our CLI program was **writing text** to a "**virtual file**" called "**standard output**".

tests/assets/enable_rich.py

@@ -0,0 +1,14 @@
+import typer
+
+typer.enable_rich(False)
+
+app = typer.Typer()
+
+
+@app.command()
+def main(arg: str):  # pragma: no cover
+    pass
+
+
+if __name__ == "__main__":
+    app()

tests/test_enable_rich.py

@@ -0,0 +1,15 @@
+import subprocess
+import sys
+from pathlib import Path
+
+
+def test_custom_prog_name():
+    file_path = Path(__file__).parent / "assets/enable_rich.py"
+    result = subprocess.run(
+        [sys.executable, "-m", "coverage", "run", str(file_path), "--help"],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        encoding="utf-8",
+    )
+    assert "Arguments:" in result.stdout  # as opposed to 'Arguments' without ':'
+    # like in the Rich Panels