README.md in trackler-2.2.1.101

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 Parallelism is about doing things in parallel that can also be done
 sequentially. A common example is counting the frequency of letters.
 Create a function that returns the total frequency of each letter in a
 list of texts and that employs parallelism.
 
+## Concurrency vs Parallelism
+
+Go supports concurrency via "[goroutines](https://golangbot.com/goroutines/)"
+which are started with the `go` keyword. It is a simple, lightweight and elegant
+way to provide concurrency support and is one of the greatest strengths of the
+language.
+
+You may notice that while this exercise is called _Parallel_ letter frequency
+you don't see the term "Parallel" used very often in Go. Gophers prefer to use
+the term **Concurrent** to describe the management of multiple independent
+goroutines ("processes" or "threads" in other language contexts). Although
+these terms are often used interchangeably Gophers like to be technically
+correct and use "concurrent" when discussing the seemingly simultaneous
+executions of goroutines.
+
+While we can plan for our programs to run in parallel, and at times they may
+appear to run in parallel, without strict knowledge of the execution context of
+our code all we can guarantee is that processes will run concurrently. In other
+words they may be executing sequentially faster than we can distinguish but not
+strictly simultaneously.
+
+For more take a look at The Go Blog's post: [Concurrency is not parallelism](https://blog.golang.org/concurrency-is-not-parallelism).
+
+## Concurrency Resources
+
+If you are new to the concurrency features in Go here are some resources to get
+you started. We recommend looking over these before starting this exercise:
+
+* [Concurrency in the Golang Book](https://www.golang-book.com/books/intro/10)
+* [A Tour of Go's concurrency section](https://tour.golang.org/concurrency/1)
+* [Go's sync.Map](https://medium.com/@deckarep/the-new-kid-in-town-gos-sync-map-de24a6bf7c2c)
+
+For a really deep dive you can try the book [Concurrency in Go](http://shop.oreilly.com/product/0636920046189.do) by [@kat-co](https://github.com/kat-co).
+
+
 ## Running the tests
 
 To run the tests run the command `go test` from within the exercise directory.
 
 If the test suite contains benchmarks, you can run these with the `-bench`