nix add-to-store: Move markdown docs into a separate file

src/nix/add-to-store.cc

@@ -38,30 +38,9 @@ struct CmdAddToStore : MixDryRun, StoreCommand
 
     std::string doc() override
     {
-        return R"(
+        return
-          # Description
+          #include "add-to-store.md"
-
+          ;
-          Copy the file or directory *path* to the Nix store, and
-          print the resulting store path on standard output.
-
-          > **Warning**
-          >
-          > The resulting store path is not registered as a garbage
-          > collector root, so it could be deleted before you have a
-          > chance to register it.
-
-          # Examples
-
-          Add a regular file to the store:
-
-          ```console
-          # echo foo > bar
-          # nix add-to-store --flat ./bar
-          /nix/store/cbv2s4bsvzjri77s2gb8g8bpcb6dpa8w-bar
-          # cat /nix/store/cbv2s4bsvzjri77s2gb8g8bpcb6dpa8w-bar
-          foo
-          ```
-        )";
     }
 
     Category category() override { return catUtility; }

src/nix/add-to-store.md

@@ -0,0 +1,28 @@
+R""(
+
+# Description
+
+Copy the file or directory *path* to the Nix store, and
+print the resulting store path on standard output.
+
+> **Warning**
+>
+> The resulting store path is not registered as a garbage
+> collector root, so it could be deleted before you have a
+> chance to register it.
+
+# Examples
+
+Add a regular file to the store:
+
+```console
+# echo foo > bar
+
+# nix add-to-store --flat ./bar
+/nix/store/cbv2s4bsvzjri77s2gb8g8bpcb6dpa8w-bar
+
+# cat /nix/store/cbv2s4bsvzjri77s2gb8g8bpcb6dpa8w-bar
+foo
+```
+
+)""