docs: Add missing period (angular#46799)

This adds a missing period in one documentation sentence.

PR Close angular#46799

Author: Ivaylo-Kirov

aio/content/guide/architecture-modules.md

@@ -1,7 +1,7 @@
 # Introduction to modules
 
 Angular applications are modular and Angular has its own modularity system called *NgModules*.
-NgModules are containers for a cohesive block of code dedicated to an application domain, a workflow, or a closely related set of capabilities
+NgModules are containers for a cohesive block of code dedicated to an application domain, a workflow, or a closely related set of capabilities.
 They can contain components, service providers, and other code files whose scope is defined by the containing NgModule.
 They can import functionality that is exported from other NgModules, and export selected functionality for use by other NgModules.