Add contributing info and code of conduct

Author: afilina

CODE_OF_CONDUCT.md

@@ -0,0 +1,25 @@
+# Contributing to PHP Legacy Docs
+
+We look forward to your contributions! You can contribute in the following ways.
+
+## Report Inaccuracies
+
+There are two options:
+
+- Click Report a Bug on the appropriate [legacy docs page](https://php-legacy-docs.zend.com) (preferred).
+- Create an [issue](https://github.com/zendtech/php-legacy-docs/issues) directly.
+
+## Propose File Changes
+
+There are two options:
+
+- Click Edit on the appropriate [legacy docs page](https://php-legacy-docs.zend.com).
+- Clone [this repository](https://github.com/zendtech/php-legacy-docs).
+
+Please always create a new branch for submitting a Pull Request.
+
+The `/styles` folder contains the CSS that will enable you to preview an HTML page before you submit the patch.
+
+Because of the large number of files, it's not practical to navigate this repository through the browser.
+
+## We have a Code of Conduct