## What is the purpose of the change

This PR is created during the Informal Systems audit, after analysis of the existing specification and code inspection
Auditing is performed on commit hash: https://github.com/osmosis-labs/osmosis/commit/42d73f1cc1c52e85561518be1014b730ef6b7a12


## Brief Changelog
- GAMM/README.md is expanded with certain details that we found important to know and understand during the creation of the TLA spec for the GAMM module
- Diagrams added for easier understanding of code structure of GAMM module base and two types of pool styles (balancer and stableswap)
- minor changes in function descriptions to hold the explanation of the actual implementation

## Testing and Verifying

*(Please pick one of the following options)*

This change is a trivial rework / code cleanup without any test coverage.

## Documentation and Release Note

  - Does this pull request introduces a new feature or user-facing behavior changes?  no
  - Is a relevant changelog entry added to the `Unreleased` section in `CHANGELOG.md`?  no
  - How is the feature or change documented?  specification x/GAMM/README.md