Merge branch 'contributing-md-file-read' into 'master'

Add an extra reference to the 'shell commands' guide

The 'shell commands' guide now also has tips on opening/reading files and handling paths.

See merge request !1321

CONTRIBUTING.md

@@ -75,6 +75,7 @@ If you can, please submit a merge request with the fix or improvements including
 1. Link relevant [issues](https://gitlab.com/gitlab-org/gitlab-ce/issues) and/or [feature requests](http://feedback.gitlab.com/) from the merge request description and leave a comment on them with a link back to the MR
 1. Be prepared to answer questions and incorporate feedback even if requests for this arrive weeks or months after your MR submission
 1. If your MR touches code that executes shell commands, make sure it adheres to the [shell command guidelines](    doc/development/shell_commands.md).
+1. Also have a look at the [shell command guidelines](doc/development/shell_commands.md) if your code reads or opens files, or handles paths to files on disk.
 
 The **official merge window** is in the beginning of the month from the 1st to the 7th day of the month. The best time to submit a MR and get feedback fast. Before this time the GitLab B.V. team is still dealing with work that is created by the monthly release such as assisting subscribers with upgrade issues, the release of Enterprise Edition and the upgrade of GitLab Cloud. After the 7th it is already getting closer to the release date of the next version. This means there is less time to fix the issues created by merging large new features.