readme: mark display managers as supported

It's been a long while since we've heard about issues related to
display managers. Some used to be unreliable in the past, but by
now most issues have been ironed out. Let's start supporting them
officially.

I've considered translating other languages but I'm concerned about
messing up the sentence. I've updated languages I'm comfortable
with.

README.fr.md

@@ -61,9 +61,7 @@ documentation pour la configuration de sway.
 
 ## Exécution
 
-Exécutez `sway` à partir d'un TTY. Certains gestionnaires d'affichage peuvent
-fonctionner, mais ne sont pas supportés par Sway (gdm est réputé pour assez
-bien fonctionner).
+Exécutez `sway` à partir d'un TTY ou d'un gestionnaires d'affichage.
 
 [Wayland]: http://wayland.freedesktop.org/
 [i3]: https://i3wm.org/

README.ko.md

@@ -52,4 +52,4 @@ i3를 이미 사용 중이라면, i3 config을 `~/.config/sway/config`로 복사
 
 ## 실행
 
-TTY에서 `sway`를 실행하세요. 일부 display manager는 작동하지만, sway로 부터 지원되지 않습니다(gdm은 상당히 잘 작동한다고 알려져 있습니다).
+TTY나 display manager에서 `sway`를 실행하세요.

README.md

@@ -53,8 +53,7 @@ Run `man 5 sway` for information on the configuration.
 
 ## Running
 
-Run `sway` from a TTY. Some display managers may work but are not supported by
-sway (gdm is known to work fairly well).
+Run `sway` from a TTY or from a display manager.
 
 [en]: https://github.com/swaywm/sway#readme
 [ar]: README.ar.md