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/add-fixed.md

@@ -0,0 +1,36 @@
+# Name
+
+`nix-store --add-fixed` - add paths to store using given hashing algorithm
+
+## Synopsis
+
+`nix-store` `--add-fixed` [`--recursive`] *algorithm* *paths…*
+
+## Description
+
+The operation `--add-fixed` adds the specified paths to the Nix store.
+Unlike `--add` paths are registered using the specified hashing
+algorithm, resulting in the same output path as a fixed-output
+derivation. This can be used for sources that are not available from a
+public url or broke since the download expression was written.
+
+This operation has the following options:
+
+- `--recursive`
+
+  Use recursive instead of flat hashing mode, used when adding
+  directories to the store.
+
+{{#include ./opt-common.md}}
+
+{{#include ../opt-common.md}}
+
+{{#include ../env-common.md}}
+
+## Example
+
+```console
+$ nix-store --add-fixed sha256 ./hello-2.10.tar.gz
+/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz
+```
+