Description front matter missing from pattern pages

[iluwatar]

Jekyll front matter is used to add attributes to web pages on our web site. All the patterns have their front matter defined in README.md but description is missing from there. description is used to add HTML meta tag to the pattern's web page as can be seen here: https://github.com/iluwatar/java-design-patterns/blob/gh-pages/_includes/head.html#L8

In this task we add description front matter to all patterns so that Google finds the pages better. Let's track the progress with the following checklist.

[ ] abstract-document
[ ] abstract-factory
[ ] acyclic-visitor
[ ] adapter
[ ] aggregator-microservices
[ ] ambassador
[ ] api-gateway
[ ] async-method-invocation
[ ] balking
[ ] bridge
[ ] builder
[ ] business-delegate
[ ] bytecode
[ ] caching
[ ] callback
[ ] chain
[ ] collection-pipeline
[ ] command
[ ] commander
[ ] composite
[ ] converter
[ ] cqrs
[ ] dao
[ ] data-bus
[ ] data-locality
[ ] data-mapper
[ ] data-transfer-object
[ ] decorator
[ ] delegation
[ ] dependency-injection
[ ] dirty-flag
[ ] double-checked-locking
[ ] double-dispatch
[ ] eip-aggregator
[ ] eip-message-channel
[ ] eip-publish-subscribe
[ ] eip-splitter
[ ] eip-wire-tap
[ ] event-aggregator
[ ] event-asynchronous
[ ] event-driven-architecture
[ ] event-queue
[ ] event-sourcing
[ ] execute-around
[ ] extension-objects
[ ] facade
[ ] factory-kit
[ ] factory-method
[ ] faq.md
[ ] feature-toggle
[ ] fluentinterface
[ ] flux
[ ] flyweight
[ ] front-controller
[ ] guarded-suspension
[ ] half-sync-half-async
[ ] hexagonal
[ ] intercepting-filter
[ ] interpreter
[ ] iterator
[ ] layers
[ ] lazy-loading
[ ] leader-election
[ ] marker
[ ] master-worker-pattern
[ ] mediator
[ ] memento
[ ] model-view-controller
[ ] model-view-presenter
[ ] module
[ ] monad
[ ] monostate
[ ] multiton
[ ] mute-idiom
[ ] mutex
[ ] naked-objects
[ ] null-object
[ ] object-mother
[ ] object-pool
[ ] observer
[ ] page-object
[ ] partial-response
[ ] pipeline
[ ] poison-pill
[ ] priority-queue
[ ] private-class-data
[ ] producer-consumer
[ ] promise
[ ] property
[ ] prototype
[ ] proxy
[ ] queue-load-leveling
[ ] reactor
[ ] reader-writer-lock
[ ] repository
[ ] resource-acquisition-is-initialization
[ ] retry
[ ] semaphore
[ ] servant
[ ] serverless
[ ] service-layer
[ ] service-locator
[ ] singleton
[ ] spatial-partition
[ ] specification
[ ] state
[ ] step-builder
[ ] strategy
[ ] template-method
[ ] thread-pool
[ ] throttling
[ ] tls
[ ] tolerant-reader
[ ] trampoline
[ ] twin
[ ] typeobjectpattern
[ ] unit-of-work
[ ] value-object
[ ] visitor

[iluwatar]

Meta tags were implemented in web site code