Add documentation on representations (#2717)

Author: sanderploegsma

exercises/shared/.docs/representations.md

@@ -0,0 +1,20 @@
+# Representations
+
+The [Java representer][github-java-representer] applies the following normalizations:
+
+- All comments are removed
+- All import declarations are removed
+- Whitespace is normalized
+- Identifiers are normalized to a placeholder value
+
+## Before you submit
+
+Please check the following things:
+
+- You don't duplicate feedback given by the analyzer.
+- You check the "examples" tab in the submit dialog and see if the feedback makes sense for all tabs.
+- You check that you have not referred to whitespace or comments.
+- You check that you don't refer to function names, or variable names as they appear in the solution, but rather use the mapping provided (or leave names out).
+  Only identifiers used by the exercise tests can be safely referred to because these are always the same for everyone.
+
+[github-java-representer]: https://github.com/exercism/java-representer