Updated Build Troubleshooting (markdown)

Build-Troubleshooting.md

@@ -51,7 +51,7 @@ MP_DEFINE_CONST_OBJ_TYPE(
     ...
 ```
 
-In most cases this change should be mechanical, pass the type, name, and flags as the first three arguments, then just replace all remaining `.a = b,` with `a, b,`. The one exception is `getiter` & `iternext`, see the next section.
+In most cases this change should be mechanical, pass the type, name, and flags as the first three arguments, then just replace all remaining `.a = b,` with `a, b,`. The two exceptions are `buffer` and `getiter` / `iternext`, see the next two sections.
 
 If your code need to access properties on a give type, e.g. `mp_type_foo.make_new` then it needs to be updated to use the accessor macros.
 
@@ -61,6 +61,30 @@ MP_OBJ_TYPE_GET_SLOT(type, slot) # equivalent to type->slot (but you must know t
 MP_OBJ_TYPE_GET_SLOT_OR_NULL(type, slot) # marginally less efficient but will return NULL if the slot is not set
 ```
 
+## buffer
+
+The definition for a type with a buffer slot has been simplified and no longer requires a nested struct.
+
+As part of updating to use `MP_DEFINE_CONST_OBJ_TYPE`, change
+
+```c
+const mp_obj_type_t mp_type_foo = {
+...
+    .buffer_p = { .get_buffer = mp_obj_str_get_buffer },
+...
+}
+```
+
+to
+
+```c
+MP_DEFINE_CONST_OBJ_TYPE(
+...
+    buffer, mp_obj_str_get_buffer,
+...
+);
+```
+
 ## getiter/iternext
 
 If you see errors about `getiter` and/or `iternext` then also see #8813.