Add transaction content (#1559)

* Update 102-transactions.md

* Update content/roadmaps/101-backend/content/108-more-about-databases/102-transactions.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/101-backend/content/108-more-about-databases/102-transactions.md

@@ -1 +1,5 @@
-# Transactions
+# Transactions
+
+In short, a database transaction is a sequence of multiple operations performed on a database, and all served as a single logical unit of work — taking place wholly or not at all. In other words, there's never a case where only half of the operations are performed and the results saved.
+
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://fauna.com/blog/database-transaction'>What are Transactions?</BadgeLink>