Consider comparing to adler32 or mentioning it in the README

[Xanewok]

I was browsing miniz_oxide dependencies when I noticed a switch at some point from a adler32 1.0.x to a 0.2.x version of this crate, which initially struck me as odd. I dug a bit and found https://github.com/Frommi/miniz_oxide/pull/83 which outlines rationale and compares the two.

I didn't initially know about the license used by adler32 and it didn't immediately occur to me that the ones used by this crate may be more desirable. Since these two crates are the implementations of Adler-32 checksum with millions of downloads by now, would you consider comparing the two or at least mentioning the key difference in the README?

Thank you for your work by the way, this crate looks great :slightly_smiling_face: