Documentation: Add alt_memery & memoist3 to performance comparison table

[pboling]

You have memery in the table already, but it has been nearly dead for a long time. alt_memery is a maintained fork I've been using in production for a while now, which has hundreds of commits on top of the old memery 1.5.0 release.

I'll work on adding alt_memery to the comparison table.

[JacobEvelyn]

Thanks for sharing! Let me know if you need help adding it.

[pboling]

Got it working. Added memoist3 (a memoist fork with Ruby3 fixes) as well! PR shortly.

[pboling]

@JacobEvelyn it is done in #339