Create Thunderbird 115 FAQ

[rtanglao]

Things to document:

• [x] colors (see "my KDE theme uses purple accent color, why TB doesn't follow it like 102 used to do?" bug reports. https://bugzilla.mozilla.org/show_bug.cgi?id=1843646#c9 and micah's comments about calendar colors )
• [x] https://blog.thunderbird.net/2023/08/make-thunderbird-yours-how-to-get-the-thunderbird-115-supernova-look/
• [x] add screenshots and links to the animated gifs from the above blog post
• [ ] known issues that we will address in the future: account colours, more customizable composer toolbar, ability to add menubar to unified toolbar, etc)
• [x] as per Wayne in matrix, add something like "Supernova is constantly evolving. Throughout the next year, we’ll deliver many improvements to existing Supernova features and introduce brand new ones. Upgrade to version 115 and experience the future of Thunderbird!"
• [x] add tbmore template from #22
• [x] incorporate Alex's feedback about colours, make it more about Linux and themes, gdoc: Thunderbird Native Linux Themeing -> DONE in revision 266774
• [ ] Add font too large/font too small FAQ as per https://github.com/thundernest/knowledgebase-issues/issues/14#issuecomment-1767168682 ; link to Thunderbird config editor article: Config Editor; add how to disable userChrome.css customizations

[rtanglao]

• WIP: https://support.mozilla.org/en-US/kb/thunderbird-115-supernova-faq

[rtanglao]

• [[T:TBMore]] added in https://support.mozilla.org/en-US/kb/thunderbird-115-supernova-faq/revision/266260

[rtanglao]

• incorporated Alex's feedback about colours, make it more about Linux and themes, gdoc: Thunderbird Native Linux Themeing -> DONE in revision 266774

[rtanglao]

font too large / too small details (from gdoc: Gigantic fonts in 115 talking points for future addition to the TB115 FAQ:

• don't think we can fix bug 1857694:"115 Supernova font / screen scaling size issues (eg oversized/huge)" and [1]: alex in comment 3: "layout.css.devPixelsPerPx is preference that comes from Firefox and we don't use nor support.Probably these users edited it in the past when Thunderbird UI wasn't really responsive nor scalable via built-in density or font size.I don't think we have any control over that pref, and we can't even ignore it." tb-support-crew and SUMO question 1424372
• Also check: ≡ > Density and ≡ > Font Size Tentative Title: Why are Thunderbird 115’s fonts so large? So small?