Merge pull request #701 from ArthurHoaro/plugins/md-html-doc

Describe markdown HTML rendering and display a warning

diff --cc plugins/markdown/README.md
index 196005e77327c61881ddeb76006825da3430a3bc,c64a831a1cb2a76f1a724889fe8fe900c0c34a94..aafcf0662ecf778da3051a44f891f5add70d3479
--- 1/plugins/markdown/README.md
--- 2/plugins/markdown/README.md
+++ b/plugins/markdown/README.md
@@@ -31,25 -32,32 +31,42 @@@ You can also add `markdown` to your lis
  This should look like:
  
  ```
 -$GLOBALS['config']['ENABLED_PLUGINS'] = array('qrcode', 'any_other_plugin', 'markdown')
 +"general": {
 +  "enabled_plugins": [
 +    "markdown",
 +    [...]
 +  ],
 +}
  ```
  
 +Parsedown parsing library is imported using Composer. If you installed Shaarli using `git`,
 +or the `master` branch, run
 +
 +    composer update --no-dev --prefer-dist
 +
  ### No Markdown tag
  
 -If the tag `.nomarkdown` is set for a shaare, it won't be converted to Markdown syntax.
 +If the tag `nomarkdown` is set for a shaare, it won't be converted to Markdown syntax.
   
 -> Note: it's a private tag (leading dot), so it won't be displayed to visitors.
 +> Note: this is a special tag, so it won't be displayed in link list.
  
+ ### HTML rendering
+ 
+ Markdown support HTML tags. For example:
+ 
+     > <strong>strong</strong><strike>strike</strike>
+    
+ Will render as:
+ 
+ > <strong>strong</strong><strike>strike</strike>
+ 
+ If you want to shaare HTML code, it is necessary to use inline code or code blocks.
+   
+ **If your shaared descriptions containing HTML tags before enabling the markdown plugin, 
+ enabling it might break your page.**
+ 
+ > Note: HTML tags such as script, iframe, etc. are disabled for security reasons.
+ 
  ### Known issue
  
  #### Redirector