docs: clarify that * in signatures does address conversion (#4681)

docs: clarify that * and $ in signatures does address conversion

It was non-obvious that `*` means the runtime does the app to native
conversion automatically. With the current docstring, one might assume
that the runtime only does boundary checks and not address conversion.
Under this assumption, passing the already-native address to
`wasm_runtime_addr_app_to_native` will lead to unexpected behavior

core/iwasm/include/wasm_export.h

@@ -1740,11 +1740,15 @@ wasm_table_type_get_max_size(const wasm_table_type_t table_type);
  *               auto check its boundary before calling the native function.
  *               If it is followed by '~', the checked length of the pointer
  *               is gotten from the following parameter, if not, the checked
- *               length of the pointer is 1.
+ *               length of the pointer is 1. The runtime will also convert
+ *               the app pointer to a native pointer, thus there is no need
+ *               to manually call `wasm_runtime_addr_app_to_native`.
  *          '~': the parameter is the pointer's length with i32 type, and must
  *               follow after '*'
  *          '$': the parameter is a string (i32 in WASM), and runtime will
- *               auto check its boundary before calling the native function
+ *               auto check its boundary before calling the native function.
+ *               Like '*', the runtime will also convert the app pointer to a
+ *               native pointer.
  * @param n_native_symbols specifies the number of native symbols in the array
  *
  * @return true if success, false otherwise