DOC: change link to contributing guide in README.md
xref https://github.com/pandas-dev/pandas/pull/32068#issuecomment-593362224
LGTM Working on the actual fix now, see #32530 Thanks @datapythonista  > Can you leave the dev. for now? (until we have a proper place for the dev docs) The link you are changing it to now are the stable docs

updated.