fish: add fish prompt

.config/fish/functions/fish_prompt.fish

@@ -0,0 +1,18 @@
+function fish_prompt --description 'Write out the prompt'
+    set -l last_status $status
+
+    set_color $fish_color_cwd
+    echo -n (pwd)
+    set_color normal
+
+    __terlar_git_prompt
+
+    if not test $last_status -eq 0
+        set_color $fish_color_error
+        echo -n " [$status]"
+        set_color normal
+    end
+
+    echo -n '➤ '
+    set_color normal
+end