Rename doc/manual{src -> source}

This is needed to avoid this
https://github.com/mesonbuild/meson/issues/13774 when we go back to
making our subproject directory `src`.

doc/manual/src/installation/installing-docker.md

@@ -1,59 +0,0 @@
-# Using Nix within Docker
-
-To run the latest stable release of Nix with Docker run the following command:
-
-```console
-$ docker run -ti ghcr.io/nixos/nix
-Unable to find image 'ghcr.io/nixos/nix:latest' locally
-latest: Pulling from ghcr.io/nixos/nix
-5843afab3874: Pull complete
-b52bf13f109c: Pull complete
-1e2415612aa3: Pull complete
-Digest: sha256:27f6e7f60227e959ee7ece361f75d4844a40e1cc6878b6868fe30140420031ff
-Status: Downloaded newer image for ghcr.io/nixos/nix:latest
-35ca4ada6e96:/# nix --version
-nix (Nix) 2.3.12
-35ca4ada6e96:/# exit
-```
-
-# What is included in Nix's Docker image?
-
-The official Docker image is created using `pkgs.dockerTools.buildLayeredImage`
-(and not with `Dockerfile` as it is usual with Docker images). You can still
-base your custom Docker image on it as you would do with any other Docker
-image.
-
-The Docker image is also not based on any other image and includes minimal set
-of runtime dependencies that are required to use Nix:
-
- - pkgs.nix
- - pkgs.bashInteractive
- - pkgs.coreutils-full
- - pkgs.gnutar
- - pkgs.gzip
- - pkgs.gnugrep
- - pkgs.which
- - pkgs.curl
- - pkgs.less
- - pkgs.wget
- - pkgs.man
- - pkgs.cacert.out
- - pkgs.findutils
-
-# Docker image with the latest development version of Nix
-
-To get the latest image that was built by [Hydra](https://hydra.nixos.org) run
-the following command:
-
-```console
-$ curl -L https://hydra.nixos.org/job/nix/master/dockerImage.x86_64-linux/latest/download/1 | docker load
-$ docker run -ti nix:2.5pre20211105
-```
-
-You can also build a Docker image from source yourself:
-
-```console
-$ nix build ./\#hydraJobs.dockerImage.x86_64-linux
-$ docker load -i ./result/image.tar.gz
-$ docker run -ti nix:2.5pre20211105
-```