docs: add equal option to toSignal for custom value comparison (angular#64241)

PR Close angular#64241

Author: SkyZeroZx

adev/src/content/ecosystem/rxjs-interop/signals-interop.md

@@ -55,6 +55,31 @@ By default, `toSignal` automatically unsubscribes from the Observable when the c
 
 To override this behavior, you can pass the `manualCleanup` option. You can use this setting for Observables that complete themselves naturally.
 
+#### Custom equality comparison
+
+Some observables may emit values that are **equals** even though they differ by reference or minor detail. The `equal` option lets you define a **custom equal function** to determine when two consecutive values should be considered the same.
+
+When two emitted values are considered equal, the resulting signal **does not update**. This prevents redundant computations, DOM updates, or effects from re-running unnecessarily.
+
+```ts
+import { Component } from '@angular/core';
+import { toSignal } from '@angular/core/rxjs-interop';
+import { interval, map } from 'rxjs';
+
+@Component(/* ... */)
+export class EqualExample {
+  temperature$ = interval(1000).pipe(
+    map(() => ({ temperature: Math.floor(Math.random() * 3) + 20 }) ) // 20, 21, or 22 randomly
+  );
+
+  // Only update if the temperature changes
+  temperature = toSignal(this.temperature$, {
+    initialValue: { temperature : 20  },
+    equal: (prev, curr) => prev.temperature === curr.temperature
+  });
+}
+```
+
 ### Error and Completion
 
 If an Observable used in `toSignal` produces an error, that error is thrown when the signal is read.