[doc] Add fontawesome 5.14.0 for self hosting

These are the minimal needed files from the downloadable archive
fontawesome-free-5.14.0-web.zip

See https://fontawesome.com/how-to-use/on-the-web/setup/hosting-font-awesome-yourself

docs/.gitignore

@@ -5,3 +5,4 @@ _pdf
 .idea/
 vendor/
 .bundle/
+assets/*.zip

docs/_config.yml

@@ -45,6 +45,7 @@ exclude:
   - pdf-*.sh
   - pdfconfigs/
   - pdf/
+  - assets/*.zip
 
 feedback_subject_line: PMD Source Code Analyzer
 

docs/assets/fontawesome-free-5.14.0-web/LICENSE.txt

@@ -0,0 +1,34 @@
+Font Awesome Free License
+-------------------------
+
+Font Awesome Free is free, open source, and GPL friendly. You can use it for
+commercial projects, open source projects, or really almost whatever you want.
+Full Font Awesome Free license: https://fontawesome.com/license/free.
+
+# Icons: CC BY 4.0 License (https://creativecommons.org/licenses/by/4.0/)
+In the Font Awesome Free download, the CC BY 4.0 license applies to all icons
+packaged as SVG and JS file types.
+
+# Fonts: SIL OFL 1.1 License (https://scripts.sil.org/OFL)
+In the Font Awesome Free download, the SIL OFL license applies to all icons
+packaged as web and desktop font files.
+
+# Code: MIT License (https://opensource.org/licenses/MIT)
+In the Font Awesome Free download, the MIT license applies to all non-font and
+non-icon files.
+
+# Attribution
+Attribution is required by MIT, SIL OFL, and CC BY licenses. Downloaded Font
+Awesome Free files already contain embedded comments with sufficient
+attribution, so you shouldn't need to do anything additional when using these
+files normally.
+
+We've kept attribution comments terse, so we ask that you do not actively work
+to remove them from files, especially code. They're a great way for folks to
+learn about Font Awesome.
+
+# Brand Icons
+All brand icons are trademarks of their respective owners. The use of these
+trademarks does not indicate endorsement of the trademark holder by Font
+Awesome, nor vice versa. **Please do not use brand logos for any purpose except
+to represent the company, product, or service to which they refer.**