Document that user-defined functions and methods are unsupported
Fixes
@@ -317,3 +317,8 @@ Most source trees have multiple subdirectories to process. These can be handled
test_data_dir = 'data'
subdir('tests')
```
+
+User-defined functions and methods
+--
+
+Meson does not currently support user-defined functions or methods. The addition of user-defined functions would make Meson Turing-complete. Avoiding this greatly simplifies the implementation. If because of this limitation you find yourself copying and pasting code a lot you may be able to use a [`foreach` loop instead](#foreach-statements).
