updated ocamlbuild workflow wiki page

This commit https://github.com/ocsigen/eliom/commit/0846f65c9aab85ed06e629662104aed3624c4608, allow you to write only:
```
<server/*>: package(yourserverdep)
<client/*>: package(yourclientdep)
true: package(yourlibdeps)
```