Template for starting a new resource grammar (#441)

Also addressing this https://github.com/GrammaticalFramework/gf-rgl/issues/238 with a README that adds a suggested implementation order.

src/TEMPLATE/RelativeTMP.gf

@@ -0,0 +1,24 @@
+concrete RelativeTMP of Relative = CatTMP ** open
+  ResTMP, Prelude in {
+
+{-
+lin
+  -- : Cl -> RCl ;            -- such that John loves her
+  RelCl cl = cl ** {
+    } ;
+
+  -- : RP -> VP -> RCl ;
+  RelVP rp vp = {
+    } ;
+
+  -- : RP -> ClSlash -> RCl ; -- who I went with
+  RelSlash rp cls = {
+    } ;
+
+  -- : RP ;
+  IdRP = {s = "that"} ;
+
+  -- : Prep -> NP -> RP -> RP ;  -- the mother of whom
+  FunRP prep np rp =
+-}
+}