add original gruvbox theme

lua/themes/gruvbox-base16.lua

@@ -0,0 +1,18 @@
+return {
+   base00 = "282828",
+   base01 = "3c3836",
+   base02 = "504945",
+   base03 = "665c54",
+   base04 = "bdae93",
+   base05 = "d5c4a1",
+   base06 = "ebdbb2",
+   base07 = "fbf1c7",
+   base08 = "fb4934",
+   base09 = "fe8019",
+   base0A = "fabd2f",
+   base0B = "b8bb26",
+   base0C = "8ec07c",
+   base0D = "83a598",
+   base0E = "d3869b",
+   base0F = "d65d0e",
+}