Update documentation about Homebrew installation and CMake integration - Homebrew

[DataHearth]

The actual documentation is wrong. The provided command line to install nlohmann_json => brew install nlohmann_json isn't the correct one.

What is the issue you have?

The issue #1576 describe and resolved the problem. But the documentation on the github page isn't updated for Homebrew.
As said, to install the library with Homebrew, I should do:

brew tap nlohmann/json
brew install nlohmann_json

The second command isn't working properly. To resolve it, refer to the issue #1576.
So, the documentation should be with brew install nlohmann_json but with brew install nlohmann-json (note the dash instead of the underscore).

Please describe the steps to reproduce the issue.

1. Follow the steps provided by the documentation to install the lib with Homebrew
2. Check the path /usr/local/Cellar/nlohmann_json
3. The lib folder containing the cmake isn't here

What is the expected behavior?

Lib folder should be available with the CMake configuration for integration with find_package().

And what is the actual behavior instead?

Lib folder isn't present.

Which compiler and operating system are you using?

• Compiler:

Apple clang version 11.0.3 (clang-1103.0.32.62)
Target: x86_64-apple-darwin19.5.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

• Operating system:

OS: MacOS Catalina
Version: 10.15.5
Laptop: MB pro 16" (sept 2019)

• Homebrew version: 2.4.9

Which version of the library did you use?

• latest release version 3.9.0
• other release - please state the version: ___
• the develop branch

[nlohmann]

Thanks! Good catch!