Document method get_tag() for both Git and SVN (#1020)
Document method get_tag() for both Git and SVN (#1020)

* Document method get_tag() for both Git and SVN

* Added return None information in get_tag() and updated get_branch()

* Use command

* Removed raise for svn

conan-io/docs,conan-io/docs,conan-io/docs,conan-io/docs