Merge branch 'es/walken-tutorial' into pu

A tutorial on object enumeration.

Perhaps take the thing with as little tweaks as possible, retitling
it to "my first object enumeration" or something?
cf. <20190814183328.GA40797@google.com>

* es/walken-tutorial:
  SQUASH???
  documentation: add tutorial for object walking

Author: gitster

Documentation/Makefile

@@ -77,6 +77,7 @@ API_DOCS = $(patsubst %.txt,%,$(filter-out technical/api-index-skel.txt technica
 SP_ARTICLES += $(API_DOCS)
 
 TECH_DOCS += MyFirstContribution
+TECH_DOCS += MyFirstObjectWalk
 TECH_DOCS += SubmittingPatches
 TECH_DOCS += technical/hash-function-transition
 TECH_DOCS += technical/http-protocol