Add the Markdown cheatsheet and a LateX example.

Time to attack the next big dragon: geogebra.

30.about/10.contributing/page.en.md

@@ -5,14 +5,14 @@ slug: contributing
 
 ## How it works
 
-- 📖 Flat files
+- 📖 *Flat files*
   - [enhanced markdown](#enhanced-markdown) for content
   - [YAML frontmatter](https://learn.getgrav.org/15/content/headers) for metadata
-- 🦊 Continuous integration using [GitLab](https://m3p2.ljbac.com)
-- 🌎 Decentralized versioning using [Git](https://en.wikipedia.org/wiki/Git)
+- 🦊 *Continuous integration* using [GitLab (Ruby)](https://m3p2.ljbac.com)
+- 🌎 *Decentralized versioning* using [Git](https://en.wikipedia.org/wiki/Git)
   - asynchronous and offline collaboration
   - scales to thousands of contributors
-- 🚀 HTML generation using Grav (PHP)
+- 🚀 *HTML generation* using [Grav (PHP)](https://m3p2.ljbac.com/m3p2/grav-website)
   - basically the new WordPress, _but much better_
   - vibrant and growing community in 2019
 
@@ -45,8 +45,63 @@ GitLab --> |updates| Website
 
 ## Enhanced Markdown
 
+The point of Markdown (compared to raw HTML) is the _readability of the source_.
+
+
+### Markdown Cheatsheet
+
+```
+# Header like h1
+## Header like h2
+…
+###### Header like h6
+
+_italic_
+__underlined__
+*bold*
+**strong**
+~~strike-through~~
+
+Go [there](https://…)
+[Current chapter](.)
+[Parent chapter](..)
+[Sibling chapter](../another-chapter)
+[Child chapter](chapter)
+[Anchor in the page](#slug-of-header)
+
+![Description of the image](local-image.png)
+
+! blue notice
+!! green notice
+!!! orange notice
+!!!! red notice
+!!!!
+!!!! another line on the red notice
+```
+
+> More at Gitlab's [Markdown documentation](https://docs.gitlab.com/ee/user/markdown.html).
+
+
+
 ### Emoticons ✨
 
 Just type or paste the unicode character, modern browsers will do the rest.
 
-Here's a handy list: https://unicode.org/emoji/charts/full-emoji-list.html
\ No newline at end of file
+Here's a handy list: https://unicode.org/emoji/charts/full-emoji-list.html
+
+
+
+### LateX
+
+You can use LateX in the courses.
+
+For example, the following
+
+    $E = m \cdot c^2$
+
+yields $E = m \cdot c^2$
+
+!!!! Make sure you add trailing spaces to expressions like `\cdot`,
+!!!! or you'll end up with broken formulas.
+!!!!
+!!!! Generous spacing also improves the readability of the source, and costs nothing.

CONTRIBUTING.md

@@ -76,13 +76,16 @@ Right now there are not many differences between the various templates but there
 ### Markdown Cheatsheet
 
 ```
-# Header <h1>
-## Header <h2>
+# Header like h1
+## Header like h2
 …
-###### Header <h6>
+###### Header like h6
 
-*emphasis*
+_italic_
+__underlined__
+*bold*
 **strong**
+~~strike-through~~
 
 Go [there](https://…)
 [Current chapter](.)
@@ -97,7 +100,7 @@ Go [there](https://…)
 !!! orange notice
 !!!! red notice
 !!!!
-!!!! still the same red notice
+!!!! another line on the red notice
 ```
 
 > More at Gitlab's [Markdown documentation](https://docs.gitlab.com/ee/user/markdown.html).