vera++: add README file

dist/tools/vera++/README.md

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+## Overview
+
+Vera++ is a programmable tool for verification, analysis and transformation of
+C++ source code. Vera++ is mainly an engine that parses C++ source files and
+presents the result of this parsing to scripts in the form of various
+collections - the scripts are actually performing the requested tasks.
+
+## Rules
+
+Rules can be added in the `rules` folder. The default rules from Vera++ were
+added. However, it's possible to implement new rules in TCL. See
+https://bitbucket.org/verateam/vera/wiki/Rules for information about the
+available rules.
+
+# Profiles
+
+A `riot_force` profile was made for describing the set of applied rules as well as
+special parameters. A `riot` profile includes all rules that should be treated as
+warnings. In case new rules are added, they can be updated for both profiles under
+`profiles` folder.
+
+## Example usage
+Check style for all changed files changed in current branch:
+    check.sh
+
+Check all changed files and don't display the results (only exit code):
+    QUIET=1 check.sh
+
+Don't display the warnings
+    WARNING=0 check.sh