keep generated documentation in a separate directory

- helps navigating the code as it highlights which files are generated
- makes it less error prone when working incrementally
  (although this should be just fixed by building out of tree)

doc/manual/src/store/types/index.md.in

@@ -0,0 +1,42 @@
+Nix supports different types of stores. These are described below.
+
+## Store URL format
+
+Stores are specified using a URL-like syntax. For example, the command
+
+```console
+# nix path-info --store https://cache.nixos.org/ --json \
+  /nix/store/a7gvj343m05j2s32xcnwr35v31ynlypr-coreutils-9.1
+```
+
+fetches information about a store path in the HTTP binary cache
+located at https://cache.nixos.org/, which is a type of store.
+
+Store URLs can specify **store settings** using URL query strings,
+i.e. by appending `?name1=value1&name2=value2&...` to the URL. For
+instance,
+
+```
+--store ssh://machine.example.org?ssh-key=/path/to/my/key
+```
+
+tells Nix to access the store on a remote machine via the SSH
+protocol, using `/path/to/my/key` as the SSH private key. The
+supported settings for each store type are documented below.
+
+The special store URL `auto` causes Nix to automatically select a
+store as follows:
+
+* Use the [local store](#local-store) `/nix/store` if `/nix/var/nix`
+  is writable by the current user.
+
+* Otherwise, if `/nix/var/nix/daemon-socket/socket` exists, [connect
+  to the Nix daemon listening on that socket](#local-daemon-store).
+
+* Otherwise, on Linux only, use the [local chroot store](#local-store)
+  `~/.local/share/nix/root`, which will be created automatically if it
+  does not exist.
+
+* Otherwise, use the [local store](#local-store) `/nix/store`.
+
+@stores@