Feature/doc updates (#571)

* Updating PHP supported versions

* Add quick explaination on Cyclomatic Complexity

Author: JustSteveKing

docs/get-started.md

@@ -1,6 +1,6 @@
 # Get started
 
-> **Requires:** [PHP 7.2+](https://php.net/releases/)
+> **Requires:** [PHP 7.4+](https://php.net/releases/)
 
 First, install PHP Insights via the `Composer` package manager:
 ```bash

docs/insights/complexity.md

@@ -6,7 +6,7 @@ For now the Complexity section is only one Insight in one Metric:
 
 ## Cyclomatic Complexity is high <Badge text="^1.0"/> <Badge text="Complexity" type="warn"/>
 
-This insight checks complexity cyclomatic on your classes. It raises an issue if complexity is over `5`.
+This insight checks complexity cyclomatic on your classes, the lower the score the easier your code is to understand. It raises an issue if complexity is over `5`.
 
 **Insight Class**: `NunoMaduro\PhpInsights\Domain\Insights\CyclomaticComplexityIsHigh`