[merge] split out and update release process docs

[Ian Clatworthy]

Martin Pool wrote:
> The developer guide is getting pretty big, and the release documentation
> is largely separate from instructions for day to day development.  So I
> split it out, and also updated some things.  A diff for just that
> section is also attached for easier review.
> 

bb: tweak

> +   objectives, or point out an high-risk things that are best done early,

s/an/any/

> +#. If the release is the first candidate, make a new branch in PQM. (Contact RobertCollins for this step).

Now this is no longer a Wiki page, s/RobertCollins/Robert Collins/.

> +#. Update the release number in the README. (It's not there as of 0.15, but please check).

This step is obsolete and can be deleted.

> +     * For point releases (i.e. a release candidate, or an incremental fix to a released version) take everything in the relevant NEWS secion : for 0.11rc2 take everything in NEWS from the bzr 0.11rc2 line to the bzr 0.11rc1 line further down.

s/secion :/section:/

> +when the release passes end-of-life because all users should have then
> +update.

s/then update./updated by then./

> +branches on Launchpad, named like 
> +<https://code.launchpad.net/~bzr/bzrtools/packaging-dapper>
> +Preconditions for building these packages:

Full stop needed between sentences here.

Ian C.