man: clarify the role of OnBootSec= in containers

https://github.com/systemd/systemd/pull/12104#pullrequestreview-218627236

diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml
index ac00d2aec26abed8838feadc4b17d35608ec95eb..9cfb453399c1d93e5002c5a8dabb92740924e33d 100644 (file)
--- a/man/systemd.timer.xml
+++ b/man/systemd.timer.xml
@@ -124,7 +124,7 @@
               </row>
               <row>
                 <entry><varname>OnBootSec=</varname></entry>
-                <entry>Defines a timer relative to when the machine was booted up.</entry>
+                <entry>Defines a timer relative to when the machine was booted up. In containers, for the system manager instance, this is mapped to <varname>OnStartupSec=</varname>, making both equivalent.</entry>
               </row>
               <row>
                 <entry><varname>OnStartupSec=</varname></entry>