Explain abbreviations and add links (#1914)

R/describe.R

@@ -1,9 +1,12 @@
 #' describe: a BDD testing language
 #'
-#' A simple BDD DSL for writing tests. The language is similar to RSpec for
-#' Ruby or Mocha for JavaScript. BDD tests read like sentences and it should
-#' thus be easier to understand what the specification of a function/component
-#' is.
+#' A simple [behavior-driven development
+#' (BDD)](https://en.wikipedia.org/wiki/Behavior-driven_development)
+#' [domain-specific language](https://en.wikipedia.org/wiki/Domain-specific_language)
+#' for writing tests. The language is similar to [RSpec](https://rspec.info/)
+#' for Ruby or [Mocha](https://mochajs.org/) for JavaScript. BDD tests read
+#' like sentences and it should thus be easier to understand what the
+#' specification of a function/component is.
 #'
 #' Tests using the `describe` syntax not only verify the tested code, but
 #' also document its intended behaviour. Each `describe` block specifies a
@@ -12,7 +15,6 @@
 #' functions as a test and is evaluated in its own environment. You
 #' can also have nested `describe` blocks.
 #'
-#'
 #' This test syntax helps to test the intended behaviour of your code. For
 #' example: you want to write a new function for your package. Try to describe
 #' the specification first using `describe`, before your write any code.