add installation and usage instructions for each client

Author: GyulyVGC

clients/express/README.md

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+# appguard-express
+
+[AppGuard](https://github.com/NullNet-ai/appguard-server) client for [Express](https://expressjs.com).
+
+### Installation
+
+Add the following to your `package.json`:
+
+```json
+"dependencies": {
+    "@nullnet/appguard-express": "^0.1.0"
+}
+```
+
+### Usage
+
+```typescript
+import express from 'express'
+import {createAppGuardMiddleware} from '@nullnet/appguard-express'
+
+const app = express()
+
+const appGuardMiddleware = createAppGuardMiddleware()
+
+app.get('/some-route', appGuardMiddleware, async (req, res) => {
+    res.json({message: 'Hello World'})
+})
+
+app.get('*' , appGuardMiddleware, async (req, res) => {
+    res.json({message: 'Hello World'})
+})
+
+app.listen(3000, () => {
+    console.log('Server is running on port 3000')
+})
+```
+
+A complete working example can be found [here](https://github.com/NullNet-ai/appguard-javascript-clients/blob/main/clients/express/sample/src/index.ts).
+
+### Environment variables
+
+The following environment variables must be set for the client to work:
+- `CONTROL_SERVICE_ADDR`: AppGuard server's IP address
+- `CONTROL_SERVICE_PORT`: AppGuard server's port
+- `INSTALLATION_CODE`: installation code for this client

clients/nextjs/README.md

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+# appguard-nextjs
+
+[AppGuard](https://github.com/NullNet-ai/appguard-server) client for [Next.js](https://nextjs.org).
+
+### Installation
+
+Add the following to your `package.json`:
+
+```json
+"dependencies": {
+    "@nullnet/appguard-nextjs": "^0.1.0",
+    "next": "^15.4.0-canary.67"
+}
+```
+
+Be aware that a canary version of Next.js is required to use the AppGuard middleware.
+
+### Usage
+
+In your `middleware.ts` file, you can use the AppGuard middleware as follows:
+
+```typescript
+import type {NextRequest} from 'next/server'
+import {createAppGuardMiddleware} from "../../src";
+
+let appGuardMiddleware = await createAppGuardMiddleware();
+
+export default async function middleware(request: NextRequest) {
+    return await appGuardMiddleware(request);
+}
+
+export const config = {
+    // allow Node.js runtime for middleware: https://nextjs.org/blog/next-15-2#nodejs-middleware-experimental
+    // this also requires next@canary: https://nextjs.org/docs/messages/ppr-preview
+    runtime: 'nodejs',
+};
+```
+
+A complete working example can be found [here](https://github.com/NullNet-ai/appguard-javascript-clients/blob/main/clients/nextjs/sample/src/middleware.ts).
+
+### Environment variables
+
+The following environment variables must be set for the client to work:
+- `CONTROL_SERVICE_ADDR`: AppGuard server's IP address
+- `CONTROL_SERVICE_PORT`: AppGuard server's port
+- `INSTALLATION_CODE`: installation code for this client