docs: add Homebrew installation instructions (#848)

* docs: add Homebrew installation instructions

During the "Learn how to fuzz like a pro" workshop (16.11.2022) Anish mentioned that it is possible to install echidna with Homebrew. It seems that this information is missing in the main Echidna readme. I've spent some time fighting with the docker container setup and later found out that you can simply `brew install echidna`. I think that adding this information would be helpful for beginner users like me. 

Such instruction is already present in the [building secure smart contracts repo](https://github.com/crytic/building-secure-contracts/tree/master/program-analysis/echidna#installation).

* docs: add explicit description of 1 line installation

Commit incorporates changes proposed by @elopez:
- More appropriate section title
- Info about dependencies installed with `brew install echidna`
- additional info about `echidna` Homebrew Formula

Co-authored-by: Emilio López <2642849+elopez@users.noreply.github.com>

* Update README.md

Co-authored-by: Emilio López <2642849+elopez@users.noreply.github.com>
Co-authored-by: Gustavo Grieco <31542053+ggrieco-tob@users.noreply.github.com>

README.md

@@ -178,6 +178,14 @@ EVM emulation and testing is hard. Echidna has a number of limitations in the la
 Before starting, make sure Slither is [installed](https://github.com/crytic/slither) (`pip3 install slither-analyzer --user`).
 If you want to quickly test Echidna in Linux or MacOS, we provide statically linked Linux binaries built on Ubuntu and mostly static MacOS binaries on our [releases page](https://github.com/crytic/echidna/releases). You can also grab the same type of binaries from our [CI pipeline](https://github.com/crytic/echidna/actions?query=workflow%3ACI+branch%3Amaster+event%3Apush), just click the commit to find binaries for Linux or MacOS.
 
+### Homebrew (macOS / Linux)
+
+If you have Homebrew installed on your Mac or Linux machine, you can install Echidna and all of its dependencies (Slither, crytic-compile) by running `brew install echidna`.
+
+You can also compile and install the latest `master` branch code by running `brew install --HEAD echidna`
+
+You can get further information in the [`echidna` Homebrew Formula](https://formulae.brew.sh/formula/echidna) page. The formula itself is maintained as part of the [homebrew-core repository](https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/echidna.rb)
+
 ### Docker container
 
 If you prefer to use a pre-built Docker container, check out our [docker