bug#34002: Document -xrm more

[積丹尼 Dan Jacobson]

On (info "(emacs) Resources")

‘-xrm RESOURCE-VALUES’
‘--xrm=RESOURCE-VALUES’
     This option specifies X resource values for the present Emacs job.

     RESOURCE-VALUES should have the same format that you would use
     inside a file of X resources.  To include multiple resource
     specifications in RESOURCE-VALUES, put a newline between them, just
     as you would in a file.  You can also use ‘#include "FILENAME"’ to
     include a file full of resource specifications.  Resource values
     specified with ‘-xrm’ take precedence over all other resource
     specifications.

Mention if it nullifies all Emacs entries in .Xresources, or just
overrides matching ones.

Also on man emacs

       You can set X default values for your Emacs windows in your
       .Xresources file (see xrdb(1)). Use the following format:

              emacs.keyword:value

but do mention -xrm there on the man page, so people don't have to
bother with the .Xresources file just to try a quick item.

P.S., at the bottom of the man page we see
GNU Emacs 26.1         2007 April 13          EMACS(1)
which looks new on the left but old in the middle, here on Debian.