Docs: Add build instructions to compile with AMXXPack

[rtxa]

We can add simple build instructions for newcorners with or w/o AMXXPack.

AMXXPack

• Currently, we use AMXXPack only for compiling all the plugins and output to our server folder for local testing, with watching changes (Hot reloading) to speed development.
• To output to your local server folder, just create a amxxpack.json and change the plugins and assets with your paths. For example:
  • plugins property with "C:/Users/rtxa/Documents/hlserver/valve/addons/amxmodx/plugins
  • assets property with "C:/Users/rtxa/Documents/hlserver/valve/"
• In the future, maybe we could follow AMXXPack folder structure for projects, where source fiels go in /src and assets like sounds, models, dlls, etc. go in /assets.
• Also, package everything with AMXXPack, reducing steps in GitHub Actions.
• We don't include amxxpack.json in the project repository, but in case we did, it would be desirable to ignore local changes to amxxpack.json with git update-index —assume-unchanged amxxpack.json git command.

{
  "input": {
    "scripts": "./valve/addons/amxmodx/scripting",
    "include": "./valve/addons/amxmodx/scripting/include",
    "assets": [
      {
        "dir": "./valve",
        "filter": "*.!(so|loc|inc|sma)"
      }
    ]
  },
  "output": {
    "plugins": null,
    "assets": null,
    "scripts": null,
    "include": null
  },
  "compiler": {
    "dir": "./.compiler",
    "version": "1.10",
    "executable": "amxxpc"
  },
  "thirdparty": {
    "dir": "./.thirdparty",
    "dependencies": []
  },
  "include": [],
  "rules": {
    "flatCompilation": true
  }
}