Furthermore we adapt the README and our ansible main.yml to take care of
removing File::Slurp from our build dependencies and replacing it with
Path::Tiny

The var_p/runc100 option is used to detect the version of runc we are
using. The format of the output of `runc --version` is different in both
versions, so it is not easy to parse. However I noticed that runc 0.1.1
does not exit with an error when we try to use a command that does not
exist while runc >= 1.0.0 does, so we use that to detect the runc
version we are using.

When using runc >= 1.0.0, we use `runc run` instead of `runc start':
https://github.com/opencontainers/runc/commit/c669b8d1568633c68bd915561ceb2e5ecc1bfc6a

In the runc config.json file, the format of the capabilities has been
changed. Instead of having one list of capabilities, there are now
separate lists for bounding, effective, inheritable, permitted and
ambient capabilities (and we use the same list for all of them):
https://github.com/opencontainers/runtime-spec/commit/eb114f057094dd2314682d55f8cb9c189915ac86

We also add /proc/timer_list and /sys/firmware to the "maskedPaths", as
those paths are now listed by default in the config.json file generated
by `runc spec` with runc 1.0.0.

And buildconf/nb_procs to buildconf/num_procs.

Add a file to list the main things to know when making changes to the
Tor Browser build.

There is no runc package available on Ubuntu 14.04.

Update rbm and add example rbm.local.conf file.