Create tree-sitter-r-tags.scm

Add tags.scm file for R, from 
https://github.com/r-lib/tree-sitter-r/blob/main/queries/tags.scm
(which has MIT licence, as already mentioned in the readme)

aider/queries/tree-sitter-r-tags.scm

@@ -0,0 +1,21 @@
+(binary_operator
+    lhs: (identifier) @name
+    operator: "<-"
+    rhs: (function_definition)
+) @definition.function
+
+(binary_operator
+    lhs: (identifier) @name
+    operator: "="
+    rhs: (function_definition)
+) @definition.function
+
+(call
+    function: (identifier) @name
+) @reference.call
+
+(call
+    function: (namespace_operator
+        rhs: (identifier) @name
+    )
+) @reference.call