It would be great to have an option for typing in tengwar. Of course, we can always just type in tengwar:
But then, the correct display is up to anybody who reads the post.
Of course, the encoding is the real challenge, since tengwar isn’t included in unicode. If you have the patience for LaTeX and thus not actually typing in tengwar, but instead stuff like /Toore/TTthreedots/TTdorbelow, you can get very precise layout with the TengwarScript LaTeX package (https://ctan.org/pkg/tengwarscript?lang=en)
If we agree on a PUA encoding, a CSS solution is possible. It is what Tecendil does (e.g. or a few message boards (e.g. tolkienforum.de or sindarin.de). But I do not know whether custom CSS is possible here.
Otherwise, browsers can be tweaked to apply the custom CSS that allows displaying PUA tengwar. That is of course less ideal since it requires tech-savy user interaction before the tengwar can be read.
Do I have to install something to be able to read that?
You really need two things. First, a font that can display the characters, e.g. one of the Free Tengwar Font Project fonts (disclaimer: I am one of the initiators). And then, instructions that tell your viewer to use the font.
It would be most convenient if these two things could be provided server side. This should be possible (it is what Tecendil does), but we would have to convince the good folks from sdf.org to do it for us.
When using an internet browser, both the font and the instructions could be included in a custom user style script to be installed with a user style browser add-on.
When you are using an app, the app might be tweaked to provide the font. I doubt that there are apps where you can select a custom font, so this would probably mean some app development.
Otherwise, you can always paste the text into the input field of https://tecendil.com where it will be displayed correctly (the output field might garble it up, though).