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/source/command-ref/nix-store/dump-db.md

@@ -0,0 +1,26 @@
+# Name
+
+`nix-store --dump-db` - export Nix database
+
+# Synopsis
+
+`nix-store` `--dump-db` [*paths…*]
+
+# Description
+
+The operation `--dump-db` writes a dump of the Nix database to standard
+output. It can be loaded into an empty Nix store using `--load-db`. This
+is useful for making backups and when migrating to different database
+schemas.
+
+By default, `--dump-db` will dump the entire Nix database. When one or
+more store paths is passed, only the subset of the Nix database for
+those store paths is dumped. As with `--export`, the user is responsible
+for passing all the store paths for a closure. See `--export` for an
+example.
+
+{{#include ./opt-common.md}}
+
+{{#include ../opt-common.md}}
+
+{{#include ../env-common.md}}