Added CONTRIBUTING guidelines

Author: fzipi

CONTRIBUTING.md

@@ -0,0 +1,75 @@
+# Contributing to the CRS
+
+We value third-party contributions. To keep things simple for you and us,
+please adhere to the following contributing guidelines.
+
+## Getting Started
+
+* You will need a [GitHub account](https://github.com/signup/free).
+* Submit a [ticket for your issue](https://github.com/SpiderLabs/owasp-modsecurity-crs/issues), assuming one does not already exist.
+  * Clearly describe the issue including steps to reproduce when it is a bug.
+  * Make sure you specify the version that you know has the issue.
+  * Bonus points for submitting a failing test along with the ticket.
+* If you don't have push access, fork the repository on GitHub.
+
+## Making Changes
+
+* Please base your changes on branch ```v3.1/dev```
+* Create a topic branch for your feature or bug fix.
+* Make commits of logical units.
+* Make sure your commits adhere to the rules guidelines below.
+* Make sure your commit messages are in the [proper format](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html): The first line of the message should have 50 characters or less, separated by a blank line from the (optional) body. The body should be wrapped at 70 characters and paragraphs separated by blank lines. Bulleted lists are also fine.
+
+## General Formatting Guidelines for rules contributions
+
+ - 4 spaces per indentation level, no tabs
+ - no trailing whitespace at EOL or trailing blank lines at EOF
+ - comments are good, especially when they clearly explain the rule
+ - try to adhere to a 80 character line length limit
+ - if it is a [chained rule](https://github.com/SpiderLabs/ModSecurity/wiki/Reference-Manual#chain), alignment should be like
+```
+    SecRule .. ..\
+        "...."
+        SecRule .. ..\
+            "..."
+            SecRule .. ..\
+                ".."
+```
+ - use quotes even if there is only one action, it improves readability (e.g use `"chain"`, not `chain`, or `"ctl:requestBodyAccess=Off"` instead of `ctl:requestBodyAccess=Off`)
+ - always use numbers for phases, instead of names
+ - format your `SecMarker` between double quotes, using UPPERCASE and separating words using hyphens. Examples are
+```
+    SecMarker "END-RESPONSE-959-BLOCKING-EVALUATION"
+    SecMarker "END-REQUEST-910-IP-REPUTATION"
+```
+ - the proposed order for actions is:
+```
+    id
+    phase
+    disruptive-action
+    status
+    capture
+    t:xxx
+    log
+    nolog
+    auditlog
+    noauditlog
+    msg
+    logdata
+    tag
+    sanitiseArg
+    sanitiseRequestHeader
+    sanitiseMatched
+    sanitiseMatchedBytes
+    ctl
+    setenv
+    setvar
+    chain
+    skip
+    skipAfter
+```
+
+FIXME:
+
+- Add rule id numbering
+- Add naming conventions for vars