Add support-vc707.md

[cmx-Y]

This PR aims to make firesim support VC707 for subsequent work.
The subsequent migrating work is roughly expected to proceed as follows:

1. Install the VCU128 board on the local host.
2. Imitate the process of generating bitstream for the vcu118 board by the firesim buildbitstream command to generate vcu128 and vc707 bitstream.
3. After generating the bitstream, try to manually program the vcu128 and vc707 board and test it.
4. After the manual test is completed, try to write the automated process into the firesim python program.
5. The files that need to be modified and added have been placed in the commit 2aa09a4.