bring back images for contributing

Author: Remi-Gau

.gitignore

@@ -5,7 +5,6 @@ tmp*
 *.zip*
 
 *.jpg
-*.png
 *.ps
 
 *.log

CONTRIBUTING.md

@@ -307,14 +307,14 @@ Upon opening the pull request we see a detailed description of what this pull
 request is seeking to address. Descriptions are important for reviewers and the
 community to gain context into what the pull request is achieving.
 
-![BIDS-pr](images/BIDS_pr.png "BIDS_pr")
+![BIDS-pr](docs/commenting_images/BIDS_pr.png "BIDS_pr")
 
 ### Generally commenting on a pull request
 
 At the bottom of the pull request page, a comment box is provided for general
 comments and questions.
 
-![BIDS-comment](images/BIDS_comment.png "BIDS-comment")
+![BIDS-comment](docs/commenting_images/BIDS_comment.png "BIDS-comment")
 
 ### Specific comments on a pull request
 
@@ -325,27 +325,27 @@ before each removed line. To comment on a specific line, hover over it, and
 click the blue plus sign (pictured below). Multiple lines can be selected by
 clicking and dragging the plus sign.
 
-![BIDS-specific-comment](images/BIDS_file_comment.png "BIDS-specific-comment")
+![BIDS-specific-comment](docs/commenting_images/BIDS_file_comment.png "BIDS-specific-comment")
 
 #### Suggesting text
 
 Comments on lines can contain "suggestions", which allow you to propose specific
 wording for consideration. To make a suggestion, click the plus/minus (±) icon
 in the comment box (pictured below).
 
-![BIDS-suggest-box](images/BIDS_suggest.png "BIDS-suggest")
+![BIDS-suggest-box](docs/commenting_images/BIDS_suggest.png "BIDS-suggest")
 
 Once the button is clicked the highlighted text will be copied into the comment
 box and formatted as a
 [Markdown code block](https://help.github.com/en/github/writing-on-github/creating-and-highlighting-code-blocks).
 
-![BIDS-suggest-text](images/BIDS_suggest_text.png "BIDS-suggest-box")
+![BIDS-suggest-text](docs/commenting_images/BIDS_suggest_text.png "BIDS-suggest-box")
 
 The "Preview" tab in the comment box will show your suggestion as it will be
 rendered. The "Suggested change" box will highlight the differences between the
 original text and your suggestion.
 
-![BIDS-suggest-change](images/BIDS_suggest_change.png "BIDS-suggest-change")
+![BIDS-suggest-change](docs/commenting_images/BIDS_suggest_change.png "BIDS-suggest-change")
 
 A comment may be submitted on its own by clicking "Add single comment". Several
 comments may be grouped by clicking "Start a review". As more comments are
@@ -364,26 +364,26 @@ their contribution.
 To do this, you must click on the `Files changed` tab at the top of the page of
 a pull request.
 
-![BIDS_pr_files_changed](images/BIDS_pr_files_changed.png "BIDS_pr_files_changed")
+![BIDS_pr_files_changed](docs/commenting_images/BIDS_pr_files_changed.png "BIDS_pr_files_changed")
 
 From there you can browse the different files changed and the 'diff' for each of
 them (what line was changed and what the change consist of). You can also see
 comments and directly change suggestions made by reviewers.
 
 You can add each suggestion one by one or group them together in a batch.
 
-![BIDS_pr_accept_comment](images/BIDS_pr_accept_comment.png "BIDS_pr_accept_comment")
+![BIDS_pr_accept_comment](docs/commenting_images/BIDS_pr_accept_comment.png "BIDS_pr_accept_comment")
 
 If you decide to batch the suggestions to add several of them at once, you must
 scroll back to the top of the 'Files changed' page and the `commit suggestions`
 button will let you add all those suggestions as a single commit.
 
-![BIDS_pr_commit_batch](images/BIDS_pr_commit_batch.png "BIDS_pr_commit_batch")
+![BIDS_pr_commit_batch](docs/commenting_images/BIDS_pr_commit_batch.png "BIDS_pr_commit_batch")
 
 Once those suggestions are committed the commit information should mention the
 reviewer as a co-author.
 
-![BIDS_pr_reviewer_credit](images/BIDS_pr_reviewer_credit.png "BIDS_pr_reviewer_credit")
+![BIDS_pr_reviewer_credit](docs/commenting_images/BIDS_pr_reviewer_credit.png "BIDS_pr_reviewer_credit")
 
 ## How the decision to merge a pull request is made?