docs: proc.rst: comm: mention the included NUL

Indicate that the actual value will be one character less.
Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
Link: https://lore.kernel.org/r/20240205154100.736499-1-mail@christoph.anton.mitterer.name
[jc: did s/null/NUL/ ]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/proc.rst

@@ -1899,8 +1899,8 @@ For more information on mount propagation see:
 These files provide a method to access a task's comm value. It also allows for
 a task to set its own or one of its thread siblings comm value. The comm value
 is limited in size compared to the cmdline value, so writing anything longer
-then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
-comm value.
+then the kernel's TASK_COMM_LEN (currently 16 chars, including the NUL
+terminator) will result in a truncated comm value.
 
 
 3.7	/proc/<pid>/task/<tid>/children - Information about task children