Bump buildroot to 2019.02

bsp/buildroot/docs/manual/adding-packages-luarocks.txt

@@ -50,6 +50,16 @@ Finally, on line 16, we invoke the +luarocks-package+
 macro that generates all the Makefile rules that actually allows the
 package to be built.
 
+Most of these details can be retrieved from the +rock+ and +rockspec+.
+So, this file and the Config.in file can be generated by running the
+command +luarocks buildroot foo lua-foo+ in the Buildroot
+directory. This command runs a specific Buildroot addon of +luarocks+
+that will automatically generate a Buildroot package. The result must
+still be manually inspected and possibly modified.
+
+* The +package/Config.in+ file has to be updated manually to include the
+  generated Config.in files.
+
 [[luarocks-package-reference]]
 
 ==== +luarocks-package+ reference