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-prefetch-url.md

@@ -0,0 +1,86 @@
+# Name
+
+`nix-prefetch-url` - copy a file from a URL into the store and print its hash
+
+# Synopsis
+
+`nix-prefetch-url` *url* [*hash*]
+  [`--type` *hashAlgo*]
+  [`--print-path`]
+  [`--unpack`]
+  [`--name` *name*]
+
+# Description
+
+The command `nix-prefetch-url` downloads the file referenced by the URL
+*url*, prints its cryptographic hash, and copies it into the Nix store.
+The file name in the store is `hash-baseName`, where *baseName* is
+everything following the final slash in *url*.
+
+This command is just a convenience for Nix expression writers. Often a
+Nix expression fetches some source distribution from the network using
+the `fetchurl` expression contained in Nixpkgs. However, `fetchurl`
+requires a cryptographic hash. If you don't know the hash, you would
+have to download the file first, and then `fetchurl` would download it
+again when you build your Nix expression. Since `fetchurl` uses the same
+name for the downloaded file as `nix-prefetch-url`, the redundant
+download can be avoided.
+
+If *hash* is specified, then a download is not performed if the Nix
+store already contains a file with the same hash and base name.
+Otherwise, the file is downloaded, and an error is signaled if the
+actual hash of the file does not match the specified hash.
+
+This command prints the hash on standard output.
+The hash is printed using base-32 unless `--type md5` is specified,
+in which case it's printed using base-16.
+Additionally, if the option `--print-path` is used,
+the path of the downloaded file in the Nix store is also printed.
+
+# Options
+
+- `--type` *hashAlgo*
+
+  Use the specified cryptographic hash algorithm,
+  which can be one of `md5`, `sha1`, `sha256`, and `sha512`.
+  The default is `sha256`.
+
+- `--print-path`
+
+  Print the store path of the downloaded file on standard output.
+
+- `--unpack`
+
+  Unpack the archive (which must be a tarball or zip file) and add the
+  result to the Nix store. The resulting hash can be used with
+  functions such as Nixpkgs’s `fetchzip` or `fetchFromGitHub`.
+
+- `--executable`
+
+  Set the executable bit on the downloaded file.
+
+- `--name` *name*
+
+  Override the name of the file in the Nix store. By default, this is
+  `hash-basename`, where *basename* is the last component of *url*.
+  Overriding the name is necessary when *basename* contains characters
+  that are not allowed in Nix store paths.
+
+# Examples
+
+```console
+$ nix-prefetch-url ftp://ftp.gnu.org/pub/gnu/hello/hello-2.10.tar.gz
+0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
+```
+
+```console
+$ nix-prefetch-url --print-path mirror://gnu/hello/hello-2.10.tar.gz
+0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
+/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz
+```
+
+```console
+$ nix-prefetch-url --unpack --print-path https://github.com/NixOS/patchelf/archive/0.8.tar.gz
+079agjlv0hrv7fxnx9ngipx14gyncbkllxrp9cccnh3a50fxcmy7
+/nix/store/19zrmhm3m40xxaw81c8cqm6aljgrnwj2-0.8.tar.gz
+```