wiki: Clarify that environment isn't imported to systemd

Author: YaLTeR

docs/wiki/Application-Issues.md

@@ -69,6 +69,9 @@ environment {
 }
 ```
 
+Note that the niri environment config does not propagate to apps and shells started by systemd, for example to DankMaterialShell and its application launcher.
+You can set the variable in your login shell config (i.e. `~/.bash_profile`) instead, though keep in mind that then it will be set for all compositors, not just niri.
+
 ### Fullscreen games
 
 Some video games, both Linux-native and on Wine, have various issues when using non-stacking desktop environments.

docs/wiki/Configuration:-Miscellaneous.md

@@ -141,6 +141,13 @@ environment {
 }
 ```
 
+Note that these variables do not propagate to the systemd global environment, so tools and applications started by systemd do not see them.
+In particular, if you start a desktop shell like DankMaterialShell through systemd, then use its built-in application launcher, the apps won't see these environment variables.
+
+If you want all processes to see the environment variables, you can set them in your login shell config instead (i.e. `~/.bash_profile`).
+The `niri-session` shell script runs through the login shell and imports all environment variables to systemd before starting niri.
+Keep in mind that all compositors will see variables set in the login shell, not just niri.
+
 ### `cursor`
 
 Change the theme and size of the cursor as well as set the `XCURSOR_THEME` and `XCURSOR_SIZE` environment variables.