doc: Fix extlinks %s substitution in caption

Substitutions in the caption are only supported in version 4 of
sphinx.
However, RTD uses sphinx 1.8.6

Just letting it append the value seems to work in both 1.8.6 and newer
versions.

doc/conf.py

@@ -118,8 +118,8 @@ smartquotes = False
 
 # Quickly link to issues or PRs using :issue:`...` or :pull:`...`
 extlinks = {
-    "issue": ("https://github.com/polybar/polybar/issues/%s", "#%s"),
-    "pull": ("https://github.com/polybar/polybar/pull/%s", "PR #%s"),
+    "issue": ("https://github.com/polybar/polybar/issues/%s", "#"),
+    "pull": ("https://github.com/polybar/polybar/pull/%s", "PR #"),
 }
 
 extlinks_detect_hardcoded_links = True

doc/user/modules/tray.rst

@@ -69,7 +69,8 @@ Settings
   .. note::
     This only affects the color of the individual icons and not the space in
     between, changing this setting to anything else than the bar background
-    will likely not look good.
+    will likely not look good unless the background color is also changed for
+    the rest of the tray module (e.g. with ``format-background``).
 
   :type: |type-color|
   :default: ``${root.background}``