Replace the generated manual pages on the master branch with
placeholders with instructions. The master branch is too much in flux
for anything generated from command output to be kept up to date,
and having pages from versions ago looks silly.
We can't remove them completely because `make dist` relies
on the files being present.
Resolves#20031.
Master was bumped to 0.16.99, so update the man pages too to avoid
confusion.
Tree-SHA512: 63622d6ebea2fb052ffe05fb80fe08bd627c34310a7ca22b2bc1af74003b20ab1a1fde51746ee69d401379d65232981b68541a9fc7f329e04b854507f836b19e
Wladimir J. van der Laan