doc/guides/mrbconf.rb: add `RO_DATA` configuration description;
@@ -151,9 +151,18 @@ largest value of required alignment.
## Reduce heap memory configuration
+`MRB_USE_ETEXT_RO_DATA_P`
+
+* Use `etext` and `edata` section addresses defined by the linker to detect read-only data.
+* Those addresses are widely available, but not portable, nor standardized.
+* This macro is defined by default on User-mode Linux.
+
+`MRB_NO_DEFAULT_RO_DATA_P`
+
+* Define this macro when the default `mrb_ro_data_p()` does not work for any reason.
+
`MRB_USE_CUSTOM_RO_DATA_P`
-* Takes precedence over `MRB_USE_LINK_TIME_RO_DATA_P`.
* Please try if `MRB_USE_LINK_TIME_RO_DATA_P` is not available.
* The `mrb_ro_data_p()` function is implemented by the user in an arbitrary file.
* The prototype declaration is `mrb_bool mrb_ro_data_p(const char *ptr)`.
