Update compilation instructions to install jq

[karkhaz]

No description provided.

[smowton]

I'd intended jq to be a soft dependency, so it didn't hobble people only interested in cbmc -- did that not work for you? If it did, suggest noting this is optional.

[smowton]

(for example: https://github.com/diffblue/cbmc/blob/12bce1707be235dc2f7b0f9e07f71b743015c0b4/jbmc/regression/jbmc-json-ui/Makefile)

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: c37284f).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/101277070

[kroening]

@smowton Many thanks for being considerate about the dependency war!
I think @karkhaz's wording is fine.

[kroening]

https://xkcd.com/797/

[karkhaz]

I could make it even more explicit, i.e.

You also need jq if you wish to run the test suite.

instead of

You also need jq to run the test suite.

will do this soon. Currently sorting out the mother of all rebase conflicts, so can't check this branch out until I'm done...

[kroening]

@karkhaz Note that Chris' scripting even takes care of jq missing, i.e., you could say "You also need jq if you wish to run the entire test suite."

[allredj]

⚠️
This PR failed Diffblue compatibility checks (cbmc commit: 94b66d3).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/103086040
Status will be re-evaluated on next push.
Common spurious failures:

• the cbmc commit has disappeared in the mean time (e.g. in a force-push)

• the author is not in the list of contributors (e.g. first-time contributors).

• the compatibility was already broken by an earlier merge.