home-manager: add more pass-through options

Specifically, pass through --[extra-]experimental-features to Nix.

docs/nix-flakes.adoc

@@ -18,10 +18,13 @@ Either set in `nix.conf`
 [source,bash]
 experimental-features = nix-command flakes
 +
-or pass them to `nix` by
+or pass them to `nix` and `home-manager` by
 +
 [source,console]
-nix --experimental-features "nix-command flakes" your command
+----
+$ nix --extra-experimental-features "nix-command flakes" <sub-commands>
+$ home-manager --extra-experimental-features "nix-command flakes" <sub-commands>
+----
 
 * Prepare your Home Manager configuration (`home.nix`).
 +

home-manager/home-manager

@@ -608,6 +608,14 @@ while [[ $# -gt 0 ]]; do
             PASSTHROUGH_OPTS+=("$opt" "$1" "$2")
             shift 2
             ;;
+        --experimental-features)
+            PASSTHROUGH_OPTS+=("$opt" "$1")
+            shift
+            ;;
+        --extra-experimental-features)
+            PASSTHROUGH_OPTS+=("$opt" "$1")
+            shift
+            ;;
         --no-out-link)
             NO_OUT_LINK=1
             ;;