filesystem doc out-of-date

[James Hunt]

The filesystem doc does not reflect the current reality:

https://developer.ubuntu.com/en/snappy/guides/filesystem-layout/

The latest partition details and sizes are now in the system-update.rts doc in the snappy codebase:

http://bazaar.launchpad.net/~snappy-dev/snappy/snappy/view/head:/docs/system-updates.rst

(This is written in restructured-text rather than simple markup since markup is not standardised and has no native way to represent tables (which this document uses a lot). See https://code.launchpad.net/~jamesodhunt/snappy/add-transactional-updates-doc/+merge/255719 for further details).

[David Callé (davidc3)]

Thanks James, I've integrated the new doc.

In the future, we'll need to come up with a script to make the generated html a bit more inline with the rest of d.u.c/snappy.