How-to-contribute.md

@@ -1,11 +1,71 @@
 # Send in bug reports, feature request, comments
 * [Check](https://github.com/projecthamster/hamster/issues) if a relevant issue already exists
-* If not, please feel encourage to [let us know](https://github.com/projecthamster/hamster/issues/new) :)
+* If not, please feel encouraged to [let us know](https://github.com/projecthamster/hamster/issues/new) :)
+
+  Please state the version you are using.
+  In case of a development version, this is the output of
+  ```bash
+  git describe --abbrev=40 --always --dirty=+
+  ```
+* Look out for [help wanted](https://github.com/projecthamster/hamster/labels/help%20wanted) flags.
+  You might just have the knowledge needed to overcome a difficulty.
 
-# Contribute code
-* Fork this project
-* Create a topic branch - git checkout -b my_branch
-* Push to your branch - git push origin my_branch
+# Test
+Feedback on pending [pull requests](https://github.com/projecthamster/hamster/pulls) is precious !
+
+Contributing for the first time can be a bit intimidating. But it is worth it !
+
+*Please file an issue or edit this wiki if something is not clear.*
+
+## One-shot test
+
+At the bottom of the pull request, look for a line similar to
+
+> Add more commits by pushing to the **waf-update** branch on **ederag/hamster**.
+
+to try out this pull request, the one-shot solution ([thanks Gerald](https://github.com/projecthamster/hamster/pull/421#issuecomment-520136033) !) is
+```bash
+# clone the waf-update branch of ederag/hamster, into the hamster-waf-update directory.
+git clone --branch=waf-update git@github.com:ederag/hamster.git hamster-waf-update
+# go to the newly created directory, holding the PR version
+cd hamster-waf-update
+```
+Then follow these [instructions](https://github.com/projecthamster/hamster#trying-the-development-version).
+
+Of course creating a new directory to try out any new modification can become tedious;
+it is possible to create a local clone of a fork, 
+linked to the upstream (main project, read-only) repository.
+
+## Fork
+
+* [Fork](https://help.github.com/en/articles/fork-a-repo) this project,
+   making sure to follow all the steps, until
+
+   `git remote -v` displays `fetch` and `push` lines both for `origin` and `upstream`.
+
+* In the fork clone directory, edit `.git/config`, adding the line (found in the [git book](https://git-scm.com/book/en/v2/GitHub-Maintaining-a-Project))
+  ```  
+  fetch = +refs/pull/*/head:refs/remotes/origin/pr/*
+  ```
+  It is then possible to try out PR 421 (replace by the relevant PR number) with
+  ```
+  git fetch --all
+  git checkout pr/421
+  ```
+
+## Contribute code
+
+* Before any change, it is good practice to issue
+  ```bash
+  git fetch --all  # get all information available (including upstream)
+  git checkout upstream/master  # start from the upstream master branch
+  ```
+* Create a topic branch: `git checkout -b my_branch`
+* Push to your branch - `git push origin my_branch`
+
+  or just `git push`, which will provide the correct command to use.
+
+  Follow the link that appears, or go to your github fork repo to...
 * Submit a Pull Request with your branch
 * That's it!