add 06-distributed-computing_jobs_by_key.rst (#259)

[ixcat]

fix: #259 , #348

[ixcat]

... am guessing we might want to rework the api similarly to https://github.com/datajoint/datajoint-python/pull/862 - also, this likely implies a new function that saves the truncation step as seen in the docs - thoughts on how to address in matlab? Thinking to just add a new +dj/key_hash.m

[guzman-raphael]

@ixcat Oh, missed this before. We should also update docs-parts/intro/Releases_lang1.rst to reflect the new change introduced here. Namely exposing the dj.key_hash utility.