Connecting a PC
Warning
This is a fast moving field. This information will be out of date in some detail even before you read it.

Yes, I know there are lots of home automation things to do but let's hook the Pi to the desktop because that makes everything 100 times easier and there will be enough to grey your hair and test your sanity without making editing and backing up files a problem.

My first attempt was to use cifs-utils but it was a total pain so I went with samba.
I read https://raspberrypihq.com/how-to-share-a-folder-with-a-windows-computer-from-a-raspberry-pi/
and this is what I extracted:
  sudo apt-get install samba samba-common-bin
  sudo nano /etc/samba/smb.conf               (to edit the configuration)

  workgroup = WORKGROUP                       (check this although it was already set)
  wins support = yes                          (but this wasn't)

    #[Homes]                                   (comment the whole [Homes] section out)
    #  comment......                           (etc)

  [Transfer]                                   (then append these at the end)
    comment=Shared folder with PC
    path=/home/pi
    browseable=Yes
    writeable=Yes
    only guest=no
    create mask=0777
    directory mask=0777
    public=no
  [homeassistant]
    comment=Shared folder to PC
    path=/home/homeassistant/.homeassistant
    browseable=Yes
    writeable=Yes
    only guest=no
    create mask=0777
    directory mask=0777
    public=no

save that file then we're going to establish an id that you can use to log onto the Pi from the PC

  sudo smbpasswd -a pi                        (set a password for a user called pi logging on from the pc)
  <redacted>
  <redacted>                                   (add a new password to the post-it)
At which point refreshing the PC's Network page showed raspberrypi with folders homeassistant and Transfer under it. I logged in as user pi with the password I had selected and copied some files over and it worked. Then I rebooted the pi and it all worked (if you wait). Don't forget to use chmod 0777 filename on things you want to grant full read/write access to.

Of course the next day it wasn't working. I couldn't find it unless I entered the name \\raspberrypi manually so I dragged the links to put shortcuts on the PC desktop so I don't care. Now configuration.yaml is within easy reach of my favourite text editor and, more importantly, I can copy, stick and rename files to keep an 'off pi' backup of dated configuration.yaml files so I can back-track when I inevitably break something which is, sadly, all to often.

I modified the stuff in configuration.yaml for my location et al and saved it on my PC as my first backup configuration.2018.01.08.21.45yaml
I can see me ending up with a lot of these...

Time for another cup of tea.