Add content to Android roadmap (#6555)

* [Add] Android Roadmap: Fragment content

* [Add] Android Roadmap: Dialog content

* [Add] Android Roadmap: Button content

* [Change] Modify the grammar

* Update src/data/roadmaps/android/content/fragments@2iDJrxjXOt7o2fPp2HfRl.md

* Update src/data/roadmaps/android/content/dialogs@Mtx0bY0drmaTw8sCM5YTl.md

* Update src/data/roadmaps/android/content/buttons@WhfzFOUpm0DFEj7Oeq21R.md

* Update src/data/roadmaps/android/content/buttons@WhfzFOUpm0DFEj7Oeq21R.md

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Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

src/data/roadmaps/android/content/buttons@WhfzFOUpm0DFEj7Oeq21R.md

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+# Buttons
+
+A `button` consists of text or an icon, or both, that communicates what action occurs when the user taps it.
+
+Learn more from the following resources:
+
+- [@official@Android Developers: Button](https://developer.android.com/develop/ui/views/components/button)

src/data/roadmaps/android/content/dialogs@Mtx0bY0drmaTw8sCM5YTl.md

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+# Dialogs
+
+A `DialogFragment` is a special fragment subclass that is designed for creating and hosting dialogs. Although you don't need to host your **dialog** within a fragment, doing so lets the `FragmentManager` manage the state of the dialog and automatically restore the dialog when a configuration change occurs.
+Learn more from the following resources:
+
+- [@official@Android Developers: Dialogs](https://developer.android.com/guide/fragments/dialogs)

src/data/roadmaps/android/content/fragments@2iDJrxjXOt7o2fPp2HfRl.md

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+# Fragments
+
+A `Fragment` represents a reusable portion of your app's UI. A fragment defines and manages its own layout, has its own lifecycle, and can handle its own input events. Fragments can't live on their own. They must be hosted by an activity or another fragment. The fragment’s view hierarchy becomes part of, or attaches to, the host’s view hierarchy.
+
+Visit the following resources to learn more:
+
+- [@official@Android Developers: Fragments](https://developer.android.com/guide/fragments)