docs(angular): add else content (#6716)

src/data/roadmaps/angular/content/else@ORdPDad4HWJAfcZuS-7yM.md

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 # @else
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+While the `@if` block can be helpful in many situations, it's common to also show fallback UI when the condition is not met. When you need a fallback, similar to JavaScript's else clause, add an `@else` block to accomplish the same effect.
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+Visit the following resources to learn more:
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+- [@official@Angular Official Docs - @else block](https://angular.dev/essentials/conditionals-and-loops#else-block)
+- [@article@Angular If Else Control Flow Blocks Explained](https://ultimatecourses.com/blog/angular-if-else-control-flow-blocks-explained)