Add notes on invoking Python methods in adapter macros (#5306)

Co-authored-by: Mila Page <[email protected]>

core/dbt/adapters/base/impl.py

@@ -130,9 +130,15 @@ class BaseAdapter(metaclass=AdapterMeta):
  methods are marked with a (passable) in their docstrings. Check docstrings
  for type information, etc.
 
- To implement a macro, implement "${adapter_type}__${macro_name}". in the
+ To implement a macro, implement "${adapter_type}__${macro_name}" in the
  adapter's internal project.
 
+ To invoke a method in an adapter macro, call it on the 'adapter' Jinja
+ object using dot syntax.
+
+ To invoke a method in model code, add the @available decorator atop a method
+ declaration. Methods are invoked as macros.
+
  Methods:
  - exception_handler
  - date_function