This fixes the documentation for UploadService and the README file:
* stop mentioning Chrome OS as we forked the code.
* update the histogram declaration workflow. It is not tied to Chrome's
histograms.xml file anymore.
* update the architecture explanation of metricsd. We split
metrics_daemon into two daemons and are now using binder to log
metrics.
* convert README to markdown to make it prettier when viewed in gitiles.
Bug: 26314417
Change-Id: I1e492f1211c1784e65dd4d3e473bb9aacefc3b5d
Bertrand SIMONNET