No documentation for static hit plugin

[djcarlin]

The static hit plugin doesn't have any documentation. In particular, the "disable-exact" option isn't mentioned in the git repo either: https://github.com/apache/trafficserver/blob/master/plugins/statichit/statichit.cc#L671C7-L671C20

I was trying to return a static response for any file under a particular path and needed to enable this option by specifying @pparam=--disable-exact