How to copy HTML files to include into nginx? How do I copy an index.html file into nginx?
root@mordor:/home/nicholas/docker/nginx# 
root@mordor:/home/nicholas/docker/nginx# ll
total 12
drwxrwxr-x 2 nicholas nicholas 4096 Nov 13 16:18 ./
drwxrwxr-x 3 nicholas nicholas 4096 Nov 13 16:12 ../
-rw-rw-r-- 1 nicholas nicholas   60 Nov 13 16:18 dockerfile
root@mordor:/home/nicholas/docker/nginx# 
root@mordor:/home/nicholas/docker/nginx# cat dockerfile 
FROM nginx
COPY /home/nicholas/html /usr/share/nginx/html


root@mordor:/home/nicholas/docker/nginx# 
root@mordor:/home/nicholas/docker/nginx# docker build -t some-content-nginx .
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM nginx
 ---&gt; c39a868aad02
Step 2/2 : COPY /home/nicholas/html /usr/share/nginx/html
COPY failed: stat /var/snap/docker/common/var-lib-docker/tmp/docker-builder726461098/home/nicholas/html: no such file or directory
root@mordor:/home/nicholas/docker/nginx# 
root@mordor:/home/nicholas/docker/nginx# ls /home/nicholas/html/
index.html
root@mordor:/home/nicholas/docker/nginx# 
root@mordor:/home/nicholas/docker/nginx# cat /home/nicholas/html/index.html 



index
hello world



nicholas@mordor:~/html$ 

I'm unclear on the source and destination, which might be complicated by docker having been installed from snap.

Looks like ansible has slightly clearer, at least for me, syntax:
  tasks:
  - name: &quot;Copying files&quot;
    copy:
      src: files/{{ item }}
      dest: /my/folder/
    with_items:
      - file.txt

or perhaps I'm doing something incorrectly.
The docker build command builds Docker images from a Dockerfile and a “context”. A build’s context is the set of files located in the specified PATH or URL. The build process can refer to any of the files in the context. For example, your build can use a COPY instruction to reference a file in the context.
From docker build documentation.
As you run the docker build with the . path for the context, it will try to find the folder home/nicholas/html from the context root@mordor:/home/nicholas/docker/nginx
The COPY command documentation shows some examples