Update introduction to JCMT OT documentation
Remove index.html symlink

Moved the file otintro.html to index.html instead of just having
it symlinked.  This is because CCAT duplicated the file in their
reorganisation, and we do not need two copies.  Added an
.htaccess file to redirect from otintro.html to the default
file for this directory because some pages link specifically
to otintro.html.