Clearer Readme install and usage instructions

### Describe the desired feature

The main readme seems cluttered with information that could be compressed or moved elsewhere.

I suggest decluttering the main Readme, e.g.
- remove [#executing-the-test-runner](https://github.com/crytic/echidna#executing-the-test-runner)
- move [#trophies](https://github.com/crytic/echidna#trophies) to another file
- move detailed [#installation](https://github.com/crytic/echidna#installation) to another file and replace with quick installation
- move [#debugging-performance-problems](https://github.com/crytic/echidna#debugging-performance-problems) out of file
- simplify [#configuration-options](https://github.com/crytic/echidna#configuration-options) and perhaps only keep cli options
- simplify/move [#collecting-and-visualizing-coverage](https://github.com/crytic/echidna#collecting-and-visualizing-coverage)

Some important things I would add:
- "Quick start": installation + run command at the very beginning of the readme (just a few lines, not detailed)
- "Coming from foundry": include instructions for running echidna on a foundry project (`--test-mode dapptest`)

Start by reviewing the main README and its linked sections: installation, test runner, trophies, debugging performance, configuration, and coverage. Define a smaller quick-start section near the beginning, move or simplify the detailed material, and add the requested Foundry usage instructions. Done means the README is less cluttered while installation, basic usage, and the relevant CLI guidance remain discoverable.

Written by the indexing model from the issue text.