docs: fix line breaks around elements in markdown

Ensure consistent line breaks around headings, lists and code blocks.

To make them more readable and also more portable (which could help when
previewing/converting files locally).

From the CommonMark Spec (version 0.30, published on 2021-06-19)[1]:

> 1.2 Why is a spec needed?

[...]

> 2. Is a blank line needed before a block quote or heading?  Most
>    implementations do not require the blank line.  However, this can
>    lead to unexpected results in hard-wrapped text, and also to
>    ambiguities in parsing (note that some implementations put the
>    heading inside the blockquote, while others do not).  (John Gruber
>    has also spoken in favor of requiring the blank lines.)[2]
>
> 3. Is a blank line needed before an indented code block?
>    (`Markdown.pl` requires it, but this is not mentioned in the
>    documentation, and some implementations do not require it.)

Fixes[3]:

* MD022 Headers should be surrounded by blank lines
* MD031 Fenced code blocks should be surrounded by blank lines
* MD032 Lists should be surrounded by blank lines

Environment: ruby-mdl 0.12.0-1 on Artix Linux.

[1] https://spec.commonmark.org/0.30/#why-is-a-spec-needed-
[2] http://article.gmane.org/gmane.text.markdown.general/2146
[3] https://github.com/markdownlint/markdownlint/blob/main/docs/RULES.md

1 files changed, 3 insertions, 0 deletions

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 76d3e709b..9c7dad2dc 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,6 +1,7 @@
 Welcome to firejail, and thank you for your interest in contributing!
 
 # Opening an issue:
+
 We welcome issues, whether to ask a question, provide information, request a new profile or
 feature, or to report a suspected bug or problem.
 
@@ -9,6 +10,7 @@ our [dedicated issue](https://github.com/netblue30/firejail/issues/1139).
 
 When submitting a bug report, please provide the following information so that
 we can handle the report more easily:
+
 - firejail version. If you're not sure, open a terminal and type `firejail --version`.
 - Linux distribution (so that we can try to reproduce it, if necessary).
 - If you know that the problem did not exist in an earlier version of firejail, please mention it.
@@ -28,6 +30,7 @@ We take security bugs very seriously. If you believe you have found one, please
 emailing us at netblue30@protonmail.com
 
 # Opening an pull request:
+
 Pull requests with enhancements, bugfixes or new profiles are very welcome.
 
 If you want to write a new profile, the easiest way to do this is to use the