doc: Add /proc/bootconfig to proc.rst

Add /proc/bootconfig description to Documentation/filesystems/proc.rst.

Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/all/20230731233130.424913-3-paulmck@kernel.org/

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Documentation/filesystems/proc.rst

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index c2aee55..4b9e951 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -684,6 +684,7 @@
  File         Content
  ============ ===============================================================
  apm          Advanced power management info
+ bootconfig   Kernel command line obtained from boot config	(5.5)
  buddyinfo    Kernel memory allocator information (see text)	(2.5)
  bus          Directory containing bus specific information
  cmdline      Kernel command line, both from bootloader and embedded