[Docs] Extend a bit the landing page of the docs

manual/index.md

@@ -9,15 +9,52 @@
 formatter. Out of the box it will enforce many of the guidelines
 outlined in the community [Ruby Style Guide](https://rubystyle.guide).
 
-Apart from reporting problems in your code, RuboCop can also
-automatically fix some of the problems for you.
+RuboCop packs a lot of features on top of what you'd normally expect from a
+linter:
 
-See ["Basic Usage"](basic_usage.md) to get yourself familiar with RuboCop's
-capabilities.
+* Works with every major Ruby implementation
+* Auto-correction of many of the code offenses it detects
+* Robust code formatting capabilities
+* Multiple result formatters for both interactive use and for feeding data into other tools
+* Ability to have different configuration for different parts of your codebase
+* Ability to disable certain cops only for specific files or parts of files
+* Extremely flexible configuration that allows you to adapt RuboCop to prety much every style and preference
+* It's easy to extend RuboCop with custom cops and formatters
+* A vast number of ready-made extensions (e.g. `rubocop-rails`, `rubocop-rspec`, `rubocop-performance` and `rubocop-minitest`)
+* Wide editor/IDE support
+* Many online services use RuboCop internally (e.g. HoundCI, Sider and CodeClimate)
+* Best logo/stickers ever
 
-See ["Versioning"](versioning.md) for information about RuboCop versioning,
-updates, and introduction of new cops.
+The project is closely tied to several efforts to document and promote the best practices of the Ruby community:
+
+* [Ruby Style Guide](https://rubystyle.guide/)
+* [Rails Style Guide](https://rails.rubystyle.guide/)
+* [RSpec Style Guide](https://rspec.rubystyle.guide/)
+* [Minitest Style Guide](https://minitest.rubystyle.guide/)
+
+A long-term goal of RuboCop (and its core extensions) is to cover with cops all the guidelines from the community style guides.
+
+So, what to do next? While you can peruse the documentation in whatever way you'd like here are
+a few recommendations:
 
-RuboCop is an extremely flexible tool and most aspects of its behavior
+* See ["Basic Usage"](basic_usage.md) to get yourself familiar with RuboCop's
+capabilities.
+* Adjust RuboCop to your style/preferences. RuboCop is an extremely flexible tool and most aspects of its behavior
 can be tweaked via various [configuration
 options](https://github.com/rubocop-hq/rubocop/blob/master/config/default.yml).
+* See ["Versioning"](versioning.md) for information about RuboCop versioning,
+updates, and introduction of new cops.
+* Explore the [existing extensions](extensions.md).
+
+## Philosophy
+
+Early on RuboCop aimed to be an opinionated linter/formater that adhered very closely to the Ruby Style Guide (think `gofmt` and the like).
+In those days cops supported just a single style and you couldn't even turn individual cops off. Eventually, we realized
+that in the Ruby community there were some many competing styles and preferences that it was going to be really
+challenging to find one set of defaults that makes everyone happy. Part of this was Ruby's own culture and philosophy,
+part was the lack of common standards for almost 20 years. It's hard to undo any of those, but it's also not really necessary.
+
+The early feedback we got lead us to adopt of philosophy of (extreme) configurability and flexibility, and trying to account for every *common* style
+of programming in Ruby. While we still believe that there's a lot of merit to just sticking to the community
+style guides, we acknowledge that Ruby is all about diversity and doing things the way that makes you happy. Whatever
+style preferences you have RuboCop is there for you. That's our promises and our guarantee. Within the subjective limits of sanity that is.