chore: update README layout + add contact links

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,9 @@
+---
+blank_issues_enabled: true
+contact_links:
+  - name: 💬 Github Discussions
+    url: https://github.com/piotr-semenov/parigp-lang/discussions
+    about: Please start any discussions here.
+  - name: 💬 Gitter Chat
+    url: https://matrix.to/#/#parigp-lang:gitter.im
+    about: Feel free to chat with me here.

README.md

@@ -1,5 +1,22 @@
+<!-- markdownlint-disable MD033 -->
 # PARI/GP Programming Language
 
-A Textmate language grammar for programming language of PARI/GP computer algebra system.
+<p align="center">
+    A Textmate language grammar for programming language of PARI/GP computer algebra system.
+    <br />
+    <a href="https://github.com/piotr-semenov/parigp-lang/issues/new?labels=bug&assignees=piotr-semenov">Report bug</a>
+    ·
+    <a href="https://github.com/piotr-semenov/parigp-lang/issues/new?labels=enhancement">Request feature</a>
+    <br />
+    <img alt="Grammar Coverage" src="https://raw.githubusercontent.com/piotr-semenov/parigp-lang/main/images/coverage-badge.svg" height="20" />
+    <a href="http://pari.math.u-bordeaux.fr/"><img alt="PARI/GP Logo" src="http://pari.math.u-bordeaux.fr/site_icons/PARI-GP-small.png" height="20" border="1" /></a>
+</p>
 
-![Grammar Coverage](./images/coverage-badge.svg)
+## Table of Contents
+
+- [Install into Visual Studio Code](#install-into-visual-studio-code)
+- [Install into Sublime Text 3](#install-into-sublime-text-3)
+
+## Install into Visual Studio Code
+
+## Install into Sublime Text 3