Since scdoc 1.9.1 is bugged, this updates the meson version check to
>= 1.9.2 and drops the version requirement from the README. This should
make it more obvious to users who have 1.9.1 that they need to update
scdoc to be able to compile man pages and hopefully cut down on the
duplicate issues
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
