See tpo/core/tor#40615, thanks @jim!

The blockchain-less procedure didn't work: NBXplorer was stuck and
would have seemingly never synchronized. This procedure actually
worked in the end, by doing a full rsync.

See team#33750

see nextcloud#6

This one could be interesting in the context of the multiple wikis
scenario, where they could all aggregate in a single site. But alas,
it only supports asciidoc.

Closes: #90.

but at least we're in sync with the template now

at least one user was thrown off guard and thought the docs here were
irrelevant because of this section

i actually redid the mirror procedure with this setting enabled to see
if this commit will overwrite a test commit I just did on the wiki,
let's see...

and GIT_SUBMODULE_STRATEGY as the suggested values are already used as
the default values, document instead in Design section (next commit)