Add info about missing optional dependencies

README.md

@@ -449,8 +449,13 @@ node app.js development
 sudo apt-get install imagemagick
 ```
 
-## Raster import support (optional)
+## Optional
+These are not strictly required to run CartoDB, but if you are installing CartoDB to do change something you might need them:
 
+### Frontend assets
+Have their own README and tools since they don't run on the Rails, see [lib/build/README.md](lib/build/README.md).
+
+### Raster import support
 Raster importer needs `raster2pgsql` to be in your path. You can check whether it's available by running `which raster2pgsql`. If it's not, you should link it: `$ sudo ln -s /usr/local/src/postgis-2.1.2/raster/loader/raster2pgsql /usr/bin/`.
 
 Access to temporary dir is also needed. Depending on your installation you might also need to run `chown 501:staff /usr/local/src/postgis-2.1.2/raster/loader/.libs` (maybe replacing `501:staff` with your installation /usr/local/src/postgis-2.1.2/raster/loader/ group and owner).