Add mention of version_slug parameter when using webhook (#2599)
Add mention of version_slug parameter when using webhook (#2599)

Signed-off-by: Thanh Ha <ddef40ffcf330e0c1e91b15bb1b0d4953f1680d8@linux.com>

Fixes #2138

tddv/readthedocs.org,davidfischer/readthedocs.org,pombredanne/readthedocs.org,pombredanne/readthedocs.org,tddv/readthedocs.org,safwanrahman/readthedocs.org,davidfischer/readthedocs.org,rtfd/readthedocs.org,pombredanne/readthedocs.org,tddv/readthedocs.org,safwanrahman/readthedocs.org,davidfischer/readthedocs.org,rtfd/readthedocs.org,safwanrahman/readthedocs.org,rtfd/readthedocs.org,davidfischer/readthedocs.org,safwanrahman/readthedocs.org,rtfd/readthedocs.org