update readme and links for 3.8.1 release (engine-3.8)

doc/manual/oqum/hazard/02_outputs.tex

@@ -100,7 +100,7 @@ \section{Description of hazard outputs}
 
 By default, OpenQuake will export only the statistical results, i.e. mean
 curves and quantiles. If the user requires the complete results for all
-realizations, there is a flag to specify, please see the FAQ \href{https://github.com/gem/oq-engine/blob/master/doc/faq-hazard.md}{https://github.com/gem/oq-engine/blob/master/doc/faq-hazard.md}.
+realizations, there is a flag to specify, please see the FAQ \href{https://github.com/gem/oq-engine/blob/engine-3.8/doc/faq-hazard.md}{https://github.com/gem/oq-engine/blob/engine-3.8/doc/faq-hazard.md}.
 Beware that if the logic tree contains a large number of end branches the
 process of exporting the results from each end branch can add a significant
 amount of time - possibly longer than the computation time - and result in a