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/command-ref/nix-store/serve.md

@@ -1,39 +0,0 @@
-# Name
-
-`nix-store --serve` - serve local Nix store over SSH
-
-# Synopsis
-
-`nix-store` `--serve` [`--write`]
-
-# Description
-
-The operation `--serve` provides access to the Nix store over stdin and
-stdout, and is intended to be used as a means of providing Nix store
-access to a restricted ssh user.
-
-The following flags are available:
-
-- `--write`
-
-  Allow the connected client to request the realization of
-  derivations. In effect, this can be used to make the host act as a
-  remote builder.
-
-{{#include ./opt-common.md}}
-
-{{#include ../opt-common.md}}
-
-{{#include ../env-common.md}}
-
-# Examples
-
-To turn a host into a build server, the `authorized_keys` file can be
-used to provide build access to a given SSH public key:
-
-```console
-$ cat <<EOF >>/root/.ssh/authorized_keys
-command="nice -n20 nix-store --serve --write" ssh-rsa AAAAB3NzaC1yc2EAAAA...
-EOF
-```
-