Add links in the docs to X-HEEP based cryptography projects from Poli…

…TO VLSI Lab (#504)

* Add PQC projects HEEP variants to docs

* Update project names

* Explicit X-HEEP integration

docs/source/How_to/eXtendingHEEP.md

@@ -10,6 +10,7 @@ Here you can find a list of `X-HEEP` based open-source examples. If you want to
 
 * [CGRA-X-HEEP](https://github.com/esl-epfl/cgra_x_heep): A CGRA loosely coupled with X-HEEP.
 * [F-HEEP](https://github.com/davidmallasen/F-HEEP): System integrating [fpu_ss](https://github.com/pulp-platform/fpu_ss) into X-HEEP via the eXtension interface and cv32e40x.
+* [KALIPSO](https://github.com/vlsi-lab/ntt_intt_kyber) and [KRONOS](https://github.com/vlsi-lab/keccak_integration/tree/keccak_xheep): Loosely-coupled, post-quantum cryptography accelerators for NTT/INTT and Keccak hash function integrated into X-HEEP.
 
 
 In addition, the `X-HEEP` testbench has been extended with a `DMA`, dummy `PERIPHERALs` (including the `FLASH`), and a CORE-V-XIF compatible co-processor