docs(tree-sitter): add doc checks for langs

langs being:
- elixir
- nix
- zig

modules/lang/elixir/doctor.el

@@ -0,0 +1,6 @@
+;; -*- lexical-binding: t; no-byte-compile: t; -*-
+;;; lang/elixir/doctor.el
+
+(assert! (or (not (featurep! +tree-sitter))
+             (featurep! :tools tree-sitter))
+         "This module requires (:tools tree-sitter)")

modules/lang/nix/doctor.el

@@ -7,3 +7,6 @@
 (unless (executable-find "nixfmt")
   (warn! "Couldn't find nixfmt. nix-format-buffer won't work."))
 
+(assert! (or (not (featurep! +tree-sitter))
+             (featurep! :tools tree-sitter))
+         "This module requires (:tools tree-sitter)")

modules/lang/zig/doctor.el

@@ -5,6 +5,10 @@
              (featurep! :tools lsp))
          "This module requires (:tools lsp)")
 
+(assert! (or (not (featurep! +tree-sitter))
+             (featurep! :tools tree-sitter))
+         "This module requires (:tools tree-sitter)")
+
 (unless (executable-find "zig")
   (warn! "Couldn't find zig binary"))