improve Project's first impression for new users (description)

- ✅ I have searched the issues and haven't found anything relevant
- ✅ I have read the docs

**Is your feature request related to a problem? Please describe.**

Currently, looking at [f-droid description](https://f-droid.org/packages/io.github.muntashirakon.AppManager/) of app manager, the [README](/MuntashirAkon/AppManager/#readme), as well as the [Introduction of docs](https://muntashirakon.github.io/AppManager/en/), it is not immediately conveyed to new users what is AM, why it exists and what makes it indispensable (how it can help protect user's privacy for example).

* the README lacks description (between title and list of features)
* the f-droid description is understandably outdated
* the docs Introduction is limited to
> App Manager is an advanced package manager for Android. It offers countless features

Sure the term "package manager" is accurate, but due to total absence of package managers on android & Windows (problem which AM aims to solve), a majority of potential users are unfamiliar with package managers in general and might miss the importance of this software. Above all, AM is much more than just a package manager x)

New users need to have a good first impression of AM in order to commit investing their time learning it and reading the docs.

**Describe the solution you'd like**

an improved description of AM to serve as a guided first impression.
Such description could briefly mention AM's capabilities focusing on the most important features and philosophies, instead of the full list of features as that is too long for f-droid (and changes frequently).

**Describe alternatives you've considered**

**Additional context**
Add any other context or screenshots about the feature request here.