Nginx installation documentation doesnt work.

github checkout of lua-nginx-modile
nginix version 1.19.0
openresty luajit2-2.1-20201027

I followed the instructions to install with nginx and I get this:

nginx: [alert] detected a LuaJIT version which is not OpenResty's; many optimizations will be disabled and performance will be compromised (see https://github.com/openresty/luajit2 for OpenResty's LuaJIT or, even better, consider using the OpenResty releases from https://openresty.org/en/download.html)
nginx: [alert] failed to load the 'resty.core' module (https://github.com/openresty/lua-resty-core); ensure you are using an OpenResty release from https://openresty.org/en/download.html (reason: module 'resty.core' not found:
        no field package.preload['resty.core']
        no file './resty/core.lua'
        no file '/usr/local/share/luajit-2.1.0-beta3/resty/core.lua'
        no file '/usr/local/share/lua/5.1/resty/core.lua'
        no file '/usr/local/share/lua/5.1/resty/core/init.lua'
        no file './resty/core.so'
        no file '/usr/local/lib/lua/5.1/resty/core.so'
        no file '/usr/local/lib/lua/5.1/loadall.so'
        no file './resty.so'
        no file '/usr/local/lib/lua/5.1/resty.so'
        no file '/usr/local/lib/lua/5.1/loadall.so') in /opt/fmadio/www/conf/nginx_http.conf:142

The error states to use the openresty luajit - but it is. I followed the instructions to do so. And there is no other luajit installed on the system. I have tried various different tweaks, but I cannot seem to get this to work.
It looks like resty.core is required to use this module in nginx. Is that the case?
I do not wish to add openresty (its far too big for our implementation - we cant afford large changes in files and structure). If openresty is now required I'll add my own luajit module.

Any help would be greatly appreciated.

Start by reviewing the Nginx installation instructions for lua-nginx-module and the configuration at /opt/fmadio/www/conf/nginx_http.conf:142, then reproduce the resty.core loading error with the stated Nginx and LuaJIT versions. Determine whether the instructions omit lua-resty-core or incorrectly require OpenResty, and update the documentation to make the supported setup and dependency clear.