Add 3.6 to Chisel Website (#3183)

* Add 3.6 to Chisel Website

* [website] Remove chisel/ baseUrl

Remove the "chisel/" base URL from all website links.  This is no longer
necessary once the website changes to chisel-lang.org.

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Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>