Add sway-ipc.7.scd to document IPC protocol

This add `sway-ipc.7.scd` that documents the IPC protocol.

This also increased the minimum scdoc version from 1.8.1 to 1.9.0 to
allow for table cells to be continued on the following line

README.md

@@ -40,7 +40,7 @@ Install dependencies:
 * pango
 * cairo
 * gdk-pixbuf2 \*\*
-* [scdoc](https://git.sr.ht/~sircmpwn/scdoc) >= 1.8.1 (optional: man pages) \*
+* [scdoc](https://git.sr.ht/~sircmpwn/scdoc) >= 1.9.0 (optional: man pages) \*
 * git \*
 
 _\*Compile-time dep_

meson.build

@@ -107,6 +107,7 @@ if scdoc.found()
 		'sway/sway.5.scd',
 		'sway/sway-bar.5.scd',
 		'sway/sway-input.5.scd',
+		'sway/sway-ipc.7.scd',
 		'sway/sway-output.5.scd',
 		'swaymsg/swaymsg.1.scd',
 		'swaynag/swaynag.1.scd',

sway/sway.1.scd

@@ -89,3 +89,4 @@ source contributors. For more information about sway development, see
 # SEE ALSO
 
 *sway*(5) *swaymsg*(1) *sway-input*(5) *sway-output*(5) *sway-bar*(5)
+*sway-ipc*(7)

sway/sway.5.scd

@@ -748,4 +748,4 @@ The following attributes may be matched with:
 
 # SEE ALSO
 
-*sway*(1) *sway-input*(5) *sway-output*(5) *sway-bar*(5)
+*sway*(1) *sway-input*(5) *sway-output*(5) *sway-bar*(5) *sway-ipc*(7)

swaymsg/swaymsg.1.scd

@@ -82,3 +82,7 @@ _swaymsg_ [options...] [message]
 	Subscribe to a list of event types. The argument for this type should be
 	provided in the form of a valid JSON array. If any of the types are invalid
 	or if an valid JSON array is not provided, this will result in an failure.
+
+# SEE ALSO
+
+*sway*(5) *sway-bar*(5) *sway-input*(5) *sway-output*(5) *sway-ipc*(7)