This file is indexed.

/var/lib/xkb/README.compiled is in xserver-common 2:1.19.2-1+deb9u5.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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The X server uses this directory to store the compiled version of the
current keymap and/or any scratch keymaps used by clients.  The X server
or some other tool might destroy or replace the files in this directory,
so it is not a safe place to store compiled keymaps for long periods of
time.  The default keymap for any server is usually stored in:
     X<num>-default.xkm
where <num> is the display number of the server in question, which makes
it possible for several servers *on the same host* to share the same 
directory.

Unless the X server is modified, sharing this directory between servers on
different hosts could cause problems.