Created basic NixOS and home-manager flake

hosts/Orchid/files/fish.fish

@@ -0,0 +1,21 @@
+function fish_greeting
+    if not set -q fish_greeting
+        set -l line1 (_ ':3')
+        set -g fish_greeting "$line1"
+    end
+
+    if set -q fish_private_mode
+        set -l line (_ "fish is running in private mode, history will not be persisted.")
+        if set -q fish_greeting[1]
+            set -g fish_greeting $fish_greeting\n$line
+        else
+            set -g fish_greeting $line
+        end
+    end
+
+    # The greeting used to be skipped when fish_greeting was empty (not just undefined)
+    # Keep it that way to not print superfluous newlines on old configuration
+    test -n "$fish_greeting"
+    and echo $fish_greeting
+end
+