is `doc/rc` the right place for theme files, namely `default.theme`?

Running `task` in an [Arch Linux container](https://hub.docker.com/layers/library/archlinux/latest) (after just installing it with `pacman -S task`, version 3.5.0-2) fails with:
```
Could not find file in CWD, directory of config file or search paths 'default.theme'.
```
The same version works fine on my Arch-based host. I tracked this issue down to the Arch Linux container image's `pacman` configuration (`/etc/pacman.conf`), which specifies `NoExtract` for the `/usr/share/doc` directory; however, this is where `default.theme` would be installed as of https://github.com/GothenburgBitFactory/taskwarrior/pull/4124 (`/usr/share/doc/task/rc/default.theme`).

Although I can change my container's `pacman` config to allow installation of `/usr/share/doc` files, I wonder if `doc/` is the appropriate place for theme files.

Start by comparing the packaged paths for doc/rc/default.theme and the Arch Linux /etc/pacman.conf NoExtract rule, using the reported /usr/share/doc/task/rc/default.theme location and pull request #4124 as context. Reproduce the failure in an Arch Linux container and verify that the chosen installation location lets task find default.theme without changing pacman configuration.

Written by the indexing model from the issue text.