Fixes incorrect statement about root nodes in the Merkle tree theory

[smoyer64]

**🐛 bug fix

The statement:

If the number of leaf nodes is a multiple of 2 the flat tree will only have a single root.

is incorrect and should rather state:

If the number of leaf nodes is a power of 2 the flat tree will only have a single root.

Checklist

• [x] documentation is changed or added

Context

No

Semver Changes

N/A