Contributing: tweaks, mention screenshots more prominently.

.github/CONTRIBUTING.md

@@ -25,4 +25,5 @@ If you have been using dear imgui for a while and/or have been using C/C++ for s
 ## How to create an Pull Request
 
 - If you are adding a feature, please explain the context of the change: what do you need the feature for?
+- Try to attach screenshots to clarify the context and demonstrate the feature at a glance.
 - Make sure you create a branch for the pull request. In Git, 1 PR is associated to 1 branch. If you keep pushing to the same branch after you submitted the PR, your new commits will appear in the PR.

.github/issue_template.md

@@ -9,4 +9,4 @@ ImGui::ThisIsMoreCode();
 ```
 For multiline snippets.
 
-(Clear this form before submitting your issue)
+(Clear this form before submitting your issue. Please read the CONTRIBUTING.md file!)

.github/pull_request_template.md

@@ -1,4 +1,5 @@
 - If you are adding a feature, please explain the context of the change: what do you need the feature for?
+- Try to attach screenshots to clarify the context and demonstrate the feature at a glance.
 - Make sure you create a branch for the pull request. In Git, 1 PR is associated to 1 branch. If you keep pushing to the same branch after you submitted the PR, your new commits will appear in the PR.
 - You can read [CONTRIBUTING.md](https://github.com/ocornut/imgui/blob/master/.github/CONTRIBUTING.md) for more details.