The https://p.z.cash documentation links in the source code are broken

For example, https://p.z.cash/halo2-0.1:ecc-complete-addition, found on [line 78 of ecc/chip/add.rs](https://github.com/zcash/halo2/blob/f9838c127ec9c14f6f323e0cfdc0c1392594d37f/halo2_gadgets/src/ecc/chip/add.rs#L78).

These links were originally introduced in this commit: https://github.com/zcash/halo2/commit/c1007d8c230a5312f280b5136af873f323d6dce6