Install instructions

[klauspost]

It seems like the installation instructions should be updated.

• [ ] Add go get github.com/bjwbell/gensimd
• [ ] Remove https://
• [ ] go install https://github.com/bjwbell/gensimd/simd/sse is wrong path

[bjwbell]

Sorry about that, I never tested the install directions. I'll have it fixed shortly

[klauspost]

No problem. Just wanted to put it in, so I didn't forget it.

[bjwbell]

Hopefully the new instructions are correct.