doc: switch rst `=` section underlines to `-` When using GENDOC_LOAD_CONFIGURED_EXTENSIONS=1, Mercurial's doc/gendoc.py can load extensions from outside of just the hgext directory, and pull in this doc. When added to the documentation, this should be nested inside of the following extension hierarchy: - Extensions - evolve The generated documentation has an established hierarchy of section headers, and the above uses `"` for top level, and `=` for each extension. Since gendoc just pastes it in verbatim, with `=` underlines, we get "Obsolescence Markers Discovery", "Effect Flag Experiment", and "Template keywords" as siblings to the evolve extension, instead of nested inside of it. This is not required for the string below it (that shows up with `hg help evolution`), as that is one level higher in the hierarchy (not nested inside of an "Extensions" section), so `=` is appropriate there.