Installation instructions for FASM2BELs have now been added. python3.7 also updated in Invoking.
Installation instructions for FASM2BELs have now been added. python3.7 also updated in Invoking.

Signed-off-by: Samuel Reynolds <b3d9aef90a806f83d27066444e433c2c2125fa24@gmail.com>

SymbiFlow/symbiflow-xc-fasm2bels