No hex target for grids

Yesterday I tried compiling the code for grids. The README says the following:

```
make -f clouds/bootloader/makefile hex
```

Unfortunately there is no hex target for grids. I was still able to generate the hex file by running `make -f grids/bootloader/makefile`

I don't know what would be the best option between fixing the doc or adding the hex target to the grids makefile.