Add 'How to load .clap plugin' to README.md

[NatureIsFrequency]

Took me a moment to see how to load a .clap plugin.
Could something like the following be added to the README.md for future users, cheers

How to load .clap plugin

Replace <PATH_TO_PLUGIN.clap> with your plugin path

Command line example

-p <PATH_TO_PLUGIN.clap>

Vscode launch.json example

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "(lldb) Launch",
            "type": "cppdbg",
            "request": "launch",
            "program": "${workspaceFolder}/builds/ninja-system/host/Debug/clap-host",
            "args": [],
            "stopAtEntry": false,
            "cwd": "${fileDirname}",
            "environment": [{ "name": "CLAP_HOST_FORCE_PLUGIN", "value": "<PATH_TO_PLUGIN.clap>" }],
            "externalConsole": false,
            "MIMode": "lldb"
        }
    ]
}