README: Add development guide

[e-zz]

Hi
I tried to clone the repo and fix sth myself but got stuck at installation of dependencies...

I suppose the correct way to start development is

• run npm install
• run npm run dev or npm run build

However, npm run dev gives me some error message

➜  Obsidian-Task-Genius git:(master) ✗ npm run dev  

> task-genius@9.9.0-beta.6 dev
> node esbuild.config.mjs

node:internal/errors:496
    ErrorCaptureStackTrace(err);
    ^

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/home/e-zz/WorkDir/Obsidian-Task-Genius/node_modules/esbuild-plugin-inline-worker/dist/index.js' imported from /home/e-zz/WorkDir/Obsidian-Task-Genius/esbuild.config.mjs
    at new NodeError (node:internal/errors:405:5)
    at finalizeResolution (node:internal/modules/esm/resolve:327:11)
    at moduleResolve (node:internal/modules/esm/resolve:946:10)
    at defaultResolve (node:internal/modules/esm/resolve:1132:11)
    at nextResolve (node:internal/modules/esm/loader:163:28)
    at ESMLoader.resolve (node:internal/modules/esm/loader:835:30)
    at ESMLoader.getModuleJob (node:internal/modules/esm/loader:424:18)
    at ModuleWrap.<anonymous> (node:internal/modules/esm/module_job:77:40)
    at link (node:internal/modules/esm/module_job:76:36) {
  code: 'ERR_MODULE_NOT_FOUND'
}

[Quorafind]

Soon

[bohnsopp]

Hi,
similar problem here:
...\dev-TaskGenius.obsidian\plugins\taskgenius-plugin>npm --version
11.7.0

...\dev-TaskGenius.obsidian\plugins\taskgenius-plugin>npm install
npm error code EUNSUPPORTEDPROTOCOL
npm error Unsupported URL Type "workspace:": workspace:*
npm error A complete log of this run can be found in: ...2025-12-30T14_58_33_186Z-debug-0.log

Is npn right, or do you use yarn or pnpm?

After testing pnpm I got the following error message:
 ERR_PNPM_WORKSPACE_PKG_NOT_FOUND  In : "@taskgenius/calendar@workspace:*" is in the dependencies but no package named "@taskgenius/calendar" is present in the workspace

Regards,
Sascha