Add to Known Errata (reg RCU fig 13.16)

README.md

@@ -117,6 +117,7 @@ new reader (5) see the new reality*"
             - `if (!gd_new) { *spin_unlock(&gdata_lock);* return -ENOMEM; }`
         - whoops again! `fix:writer makes copy for RCU & should free the old object only`
             - see commit # `70dd634`
+            - as well, in *Figure 13.16* right side bottom: replace the `kfree(gd_new);` with `kfree(gd);`
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