Updating docs to reflect the use of GitHub access tokens to perform tests

Author: Javier de Silóniz Sandino

docs/src/main/tut/docs.md

@@ -130,3 +130,10 @@ object ProgramEval extends github4s.ImplicitsJVM {
 ProgramEval.user1 should be ('right)
 ProgramEval.user1.toOption map (_.result.login shouldBe "rafaparadela")
 ```
+
+# Test credentials
+
+Note that for github4s to have access to the GitHub API during the test phases, you need to provide a valid access token with the right credentials (i.e.: users + gists scopes), through the sbt configuration variable "token":
+
+sbt -Dtoken=ACCESS_TOKEN_STRING
+```