docs: added discord server link to the landing page (#153)

## Description

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implemented in this PR. -->

### Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [x] Documentation update (improves or adds clarity to existing
documentation)

### Tested on

- [ ] iOS
- [ ] Android

### Testing instructions

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Include setup details if necessary. -->

### Screenshots

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### Related issues

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### Checklist

- [x] I have performed a self-review of my code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have updated the documentation accordingly
- [ ] My changes generate no new warnings

### Additional notes

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reviewers might need to understand this PR. -->

Co-authored-by: Maciej Rys <maciej.rys@swmansioncom>

Author: darthez

docs/docusaurus.config.js

@@ -68,6 +68,12 @@ const config = {
             label: 'Docs',
             position: 'right',
           },
+          {
+            'href': 'https://discord.gg/ZGqqY55qkP',
+            'position': 'right',
+            'className': 'header-discord',
+            'aria-label': 'Discord server',
+          },
           {
             'href':
               'https://github.com/software-mansion/react-native-executorch',

docs/src/css/overrides.css

@@ -66,8 +66,8 @@ table thead tr {
   height: 24px;
   width: 24px;
 
-  mask: url(/static/img/github.svg) no-repeat 100% 100%;
-  mask-size: cover;
+  mask: url(/static/img/github.svg) no-repeat center;
+  mask-size: contain;
   content: '';
 
   background-color: var(--ifm-navbar-link-color);
@@ -84,6 +84,35 @@ table thead tr {
   background-color: var(--ifm-navbar-link-hover-color);
 }
 
+@media (min-width: 996px) {
+  .header-discord {
+    margin-left: 1.5em;
+  }
+}
+
+.header-discord:before {
+  display: flex;
+  height: 24px;
+  width: 24px;
+
+  mask: url(/static/img/discord.svg) no-repeat center;
+  mask-size: contain;
+  content: '';
+
+  background-color: var(--ifm-navbar-link-color);
+}
+
+@media (max-height: 420px) {
+  .header-discord:before {
+    height: 20px;
+    width: 20px;
+  }
+}
+
+.header-discord:hover:before {
+  background-color: var(--ifm-navbar-link-hover-color);
+}
+
 .community-holder-container {
   display: flex;
   flex-wrap: wrap;