doc: README: Rework Resources section

With close to 20 different links, the Resources section was not really
easy to navigate, defeating the purpose of providing quick access to
information. Reworked the section to break it down into sub sections,
and reworded the links to make them self explanatory.

Each sub-section has been re-ordered so that most important links appear
first.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

README.rst

@@ -54,37 +54,59 @@ Resources
 
 Here's a quick summary of resources to help you find your way around:
 
-* **Help**: `Asking for Help Tips`_
+Getting Started
-* **Documentation**: http://docs.zephyrproject.org (`Getting Started Guide`_)
+---------------
-* **Source Code**: https://github.com/zephyrproject-rtos/zephyr is the main
-  repository; https://elixir.bootlin.com/zephyr/latest/source contains a
-  searchable index
-* **Releases**: https://github.com/zephyrproject-rtos/zephyr/releases
-* **Samples and example code**: see `Sample and Demo Code Examples`_
-* **Mailing Lists**: users@lists.zephyrproject.org and
-  devel@lists.zephyrproject.org are the main user and developer mailing lists,
-  respectively. You can join the developer's list and search its archives at
-  `Zephyr Development mailing list`_. The other `Zephyr mailing list
-  subgroups`_ have their own archives and sign-up pages.
-* **Chat**: Real-time chat happens in Zephyr's Discord Server. Use
-  this `Discord Invite`_ to register.
-* **Contributing**: see the `Contribution Guide`_
-* **Wiki**: `Zephyr GitHub wiki`_
-* **Issues**: https://github.com/zephyrproject-rtos/zephyr/issues
-* **Security Issues**: Email vulnerabilities@zephyrproject.org to report
-  security issues; also see our `Security`_ documentation. Security issues are
-  tracked separately at https://zephyrprojectsec.atlassian.net.
-* **Zephyr Project Website**: https://zephyrproject.org
 
-.. _Discord Invite: https://chat.zephyrproject.org
+  | 📖 `Zephyr Documentation`_
-.. _supported boards: http://docs.zephyrproject.org/latest/boards/index.html
+  | 🚀 `Getting Started Guide`_
-.. _Zephyr Documentation: http://docs.zephyrproject.org
+  | 🙋🏽 `Tips when asking for help`_
-.. _Introduction to Zephyr: http://docs.zephyrproject.org/latest/introduction/index.html
+  | 💻 `Code samples`_
-.. _Getting Started Guide: http://docs.zephyrproject.org/latest/develop/getting_started/index.html
+
-.. _Contribution Guide: http://docs.zephyrproject.org/latest/contribute/index.html
+Code and Development
-.. _Zephyr GitHub wiki: https://github.com/zephyrproject-rtos/zephyr/wiki
+--------------------
-.. _Zephyr Development mailing list: https://lists.zephyrproject.org/g/devel
+
-.. _Zephyr mailing list subgroups: https://lists.zephyrproject.org/g/main/subgroups
+  | 🌐 `Source Code Repository`_
-.. _Sample and Demo Code Examples: http://docs.zephyrproject.org/latest/samples/index.html
+  | 📦 `Releases`_
-.. _Security: http://docs.zephyrproject.org/latest/security/index.html
+  | 🤝 `Contribution Guide`_
-.. _Asking for Help Tips: https://docs.zephyrproject.org/latest/develop/getting_started/index.html#asking-for-help
+
+Community and Support
+---------------------
+
+  | 💬 `Discord Server`_ for real-time community discussions
+  | 📧 `User mailing list (users@lists.zephyrproject.org)`_
+  | 📧 `Developer mailing list (devel@lists.zephyrproject.org)`_
+  | 📬 `Other project mailing lists`_
+  | 📚 `Project Wiki`_
+
+Issue Tracking and Security
+---------------------------
+
+  | 🐛 `GitHub Issues`_
+  | 🔒 `Security documentation`_
+  | 🛡️ `Security Advisories Repository`_
+  | ⚠️ Report security vulnerabilities at vulnerabilities@zephyrproject.org
+
+Additional Resources
+--------------------
+  | 🌐 `Zephyr Project Website`_
+  | 📺 `Zephyr Tech Talks`_
+
+.. _Zephyr Project Website: https://www.zephyrproject.org
+.. _Discord Server: https://chat.zephyrproject.org
+.. _supported boards: https://docs.zephyrproject.org/latest/boards/index.html
+.. _Zephyr Documentation: https://docs.zephyrproject.org
+.. _Introduction to Zephyr: https://docs.zephyrproject.org/latest/introduction/index.html
+.. _Getting Started Guide: https://docs.zephyrproject.org/latest/develop/getting_started/index.html
+.. _Contribution Guide: https://docs.zephyrproject.org/latest/contribute/index.html
+.. _Source Code Repository: https://github.com/zephyrproject-rtos/zephyr
+.. _GitHub Issues: https://github.com/zephyrproject-rtos/zephyr/issues
+.. _Releases: https://github.com/zephyrproject-rtos/zephyr/releases
+.. _Project Wiki: https://github.com/zephyrproject-rtos/zephyr/wiki
+.. _User mailing list (users@lists.zephyrproject.org): https://lists.zephyrproject.org/g/users
+.. _Developer mailing list (devel@lists.zephyrproject.org): https://lists.zephyrproject.org/g/devel
+.. _Other project mailing lists: https://lists.zephyrproject.org/g/main/subgroups
+.. _Code samples: https://docs.zephyrproject.org/latest/samples/index.html
+.. _Security documentation: https://docs.zephyrproject.org/latest/security/index.html
+.. _Security Advisories Repository: https://github.com/zephyrproject-rtos/zephyr/security
+.. _Tips when asking for help: https://docs.zephyrproject.org/latest/develop/getting_started/index.html#asking-for-help
+.. _Zephyr Tech Talks: https://www.zephyrproject.org/tech-talks