tasks/local_index: build technical pages
tasks/local_index: build technical pages

This matches the recent change to preindex; otherwise our
fixed-up links go nowhere.

Note that in addition to tweaking the regex, we have to do a
few things to handle the subdirectory:

 - we need to tell `ls-tree` to recurse now (the preindex
   reads from octokit, which recurses by default)

 - we need to shrink the path to its basename to match
   preindex's flat view

git/git-scm.com,git/git-scm.com,jasonlong/git-scm.com,mosoft521/gitscm-next,mosoft521/gitscm-next,Mokolea/git-scm.com,mosoft521/gitscm-next,jasonlong/git-scm.com,git/git-scm.com,Mokolea/git-scm.com,jasonlong/git-scm.com,git/git-scm.com,mosoft521/gitscm-next,jasonlong/git-scm.com,Mokolea/git-scm.com,Mokolea/git-scm.com