Broken html tag in the manual

[arbipher]

There are four <span class="opam"> in the html manual(http://opam.ocaml.org/doc/Manual.html).
The reason seems to be the original md file is truncated at a certain column width (search <span at the raw file). The file on GitHub looks fine, though.

I guess the truncating may be the result of some formatting tool so I am not sure if sending a PR directly could solve the case in the future.
Therefore I make this issue.