Bugs in turbine docs

[aeyakovenko]

Problem

Turbine docs have typos and bugs. Reported by researches looking at the code and documentation.

Proposed Solution

fix them

tag @behzadnouri @jbiseda

[bw-solana]

Here are the items I've spotted that need to be cleaned up (in order of appearance from top to bottom):

1. Note that we possibly share shreds with neighbors. We will stop doing this once Redundant Turbine Path feature is enabled.
2. Layer 0 is actually a special case Root node. Layer 1 = neighborhood 0
3. Neighborhood assignment seed is derived from shred index + type
4. Include root in diagrams/explanations in Layer & Neighborhood structure sections
5. Mention or link to Redundant Turbine Path feature and how this impacts flows.
6. Typo: trails --> trials*
7. Shred group failure rate is actually computing the success rate. Add a 1 - to invert this
8. Trials number is wrong for 16:16 FEC example 64 --> 32*
9. Neighborhoods section should likely be moved under Layer and Neighborhood Structure section