Add an initial CONTRIBUTING file.

Add a standard CONTRIBUTING file which describes how you can contribute
to Wireshark. Make it Markdown with a .md extension since that's the
default in the GitLab UI and elsewhere.

CONTRIBUTING.md

@@ -0,0 +1,46 @@
+# Contributing to Wireshark
+
+<!--
+To do:
+- Provide an overview of project governance.
+- CoC?
+- Sponsorship?
+- SharkFest?
+-->
+
+Thank you for your interest in contributing to Wireshark!
+We wouldn’t be as successful as we are today without the help of our community.
+There are many ways to contribute and help improve Wireshark.
+
+## Help People Use Wireshark
+
+It’s not always obvious how to capture traffic or interpret what Wireshark shows you.
+We provide two primary ways to ask for help: the question and answer site at
+https://ask.wireshark.org/
+and a mailing list at
+[wireshark-users@wireshark.org](https://www.wireshark.org/lists/).
+Your constructive and respectful assistance is welcome in both places.
+
+## Report Issues
+
+If you run across a problem with Wireshark or have a suggestion for improvement, you’re welcome to tell us about it on our [issue tracker](https://gitlab.com/wireshark/wireshark/-/issues).
+When creating an issue, please select from one of the predefined templates and fill in each section as needed.
+You can increase the likelihood that a bug will be fixed by providing any materials or information required to replicate the issue.
+For most issues this means uploading a capture file, but please make sure that it doesn’t contain any private or sensitive information.
+
+The User’s Guide also has a section on [reporting problems](https://www.wireshark.org/docs/wsug_html_chunked/ChIntroHelp.html#_reporting_problems).
+
+## Write Code And Documentation
+
+Wireshark is primarily written in C, with the exception of the main application UI, which is written in C++.
+You can find its source code at https://gitlab.com/wireshark/wireshark/-/tree/master.
+You can set up a [build environment](https://www.wireshark.org/docs/wsdg_html_chunked/PartEnvironment.html) on Windows, UNIX, and UNIX-like platforms, including macOS and Linux.
+
+If you would like to contribute changes to Wireshark’s source code, you must create a [merge request](https://gitlab.com/wireshark/wireshark/-/merge_requests).
+Complete details on doing so can be found in the [Developer’s Guide](https://www.wireshark.org/docs/wsdg_html_chunked/ChSrcContribute.html) and on the [wiki](https://gitlab.com/wireshark/wireshark/-/wikis/Development/SubmittingPatches).
+When you submit a merge request, a series of automated tests will be run in order to ensure that compiles across different platforms and conforms to our coding guidelines.
+The change will also be manually reviewed by a core developer and will be merged when the change passes both automated and manual review.
+
+The Wireshark User’s Guide and Developer’s Guide are maintained in the [docbook directory](https://gitlab.com/wireshark/wireshark/-/tree/master/docbook) in the main repository.
+You don’t need a complete development environment to contribute to them, but you do need git and a text editor.
+Documentation updates must be made via a merge request similar to source code changes.

tools/checklicenses.py

@@ -70,6 +70,9 @@ PATH_SPECIFIC_ALLOWED_LICENSES = {
     'wimaxasncp/dictionary.dtd': [
         'UNKNOWN',
     ],
+    'CONTRIBUTING.md': [
+        'UNKNOWN',
+    ],
     'doc/': [
         'UNKNOWN',
     ],