Rewrite "About" page to better reflect Git's current position (#2103)

As discussed in #2058, Git is no longer an upstart, instead it's by far
the most widely used version control system. I have a few goals here:

1. Give the reader a broad sense for the core Git project's main values
("performance") and its history coming from the Linux kernel community
2. Communicate that Git and GitHub are different, and briefly explain
the historical relationship between the two projects
3. Talk about Git's popularity and ecosystem, which IMO are some of its
biggest strengths

I removed "Git is easy to learn" on the homepage because I'm not so sure
that's accurate, and all of the other "About" pages because they were
framed as a comparison to Subversion, and it seemed very hard to rework
them. If folks think that some of the old About content shouldn't be
deleted I'd be happy to talk about that though.

You can see it in action here: [about
page](https://jvns.github.io/git-scm.com/about),
[homepage](https://jvns.github.io/git-scm.com)

Fixes #2058

Author: dscho

assets/sass/dark-mode.scss

@@ -92,10 +92,6 @@
                 img:not(.no-filter) {
                     filter: brightness(0.9) contrast(0.6) invert(1);
                 }
-
-                ol#about-nav li a {
-                    filter: brightness(0.8);
-                }
             }
 
             img[alt="Git"] {

assets/sass/lists.scss

@@ -72,62 +72,6 @@ ul.books-list {
   }
 }
 
-ol#about-nav {
-  @extend .unstyled !optional;
-  @include clearfix;
-
-  li {
-    display: inline;
-    float: left;
-    width: 80px;
-    height: 85px;
-    padding-right: 5px;
-    margin-right: 7px;
-
-    &:last-child {
-      margin-right: 0;
-    }
-
-    a {
-      display: block;
-      width: 60px;
-      height: 80px;
-      padding: 0 15px;
-      font-size: 13px;
-      line-height: 20px;
-      text-align: center;
-      color: var(--light-font-color-darker-35);
-      opacity: 0.9;
-      @include background-image-2x($baseurl + "images/icons/nav-circles", 90px, 180px);
-
-      &.current {
-        @include background-image-2x($baseurl + "images/icons/nav-circles", 90px, 180px, 0 -90px);
-        color: var(--main-bg);
-        opacity: 1;
-      }
-
-      &.one-line {
-        height: 55px;
-        padding-top: 35px;
-      }
-
-      &.two-line {
-        height: 62px;
-        padding-top: 28px;
-      }
-
-      &.three-line {
-        height: 73px;
-        padding-top: 17px;
-      }
-
-      &:hover {
-        opacity: 1;
-      }
-    }
-  }
-}
-
 ul.stackoverflow {
   @extend .unstyled !optional;
   font-size: 12px;
@@ -168,23 +112,3 @@ table.binaries {
     border: solid 1px transparent;
   }
 }
-// Breakpoint ----
-@media (max-width: $default){
-  ol#about-nav {
-    display: flex;
-    flex-wrap: wrap;
-    justify-content: space-between;
-  }
-}
-
-@media (max-width: $mobile-m){
-  ol#about-nav {
-    justify-content: unset;
-    li {
-      padding-right: 0;
-      margin-right: 0.6rem;
-      flex-basis: 29%;
-      margin-bottom: 1rem;
-    }
-  }
-}

content/about/_index.html

@@ -1,6 +1,80 @@
 ---
-redirect_to: about/branching-and-merging
 url: /about.html
+section: "about"
 aliases:
 - /about/index.html
+- /about/branching-and-merging.html
+- /about/branching-and-merging/index.html
+- /about/data-assurance.html
+- /about/data-assurance/index.html
+- /about/distributed.html
+- /about/distributed/index.html
+- /about/free-and-open-source.html
+- /about/free-and-open-source/index.html
+- /about/small-and-fast.html
+- /about/small-and-fast/index.html
+- /about/staging-area.html
+- /about/staging-area/index.html
 ---
+
+<div id="main">
+<h1> About Git </h1>
+
+<h2> Git is fast </h2>
+
+<p>
+Git was built to work on the Linux kernel, meaning that it was built to handle
+repositories with tens of millions of lines of code from the start.
+Speed and performance has always been a primary design goal of Git.
+</p>
+
+<p>
+Git also stores repository history efficiently. As of 2025, the current version
+of the Linux kernel's source code is 1.7 GB.
+Git stores the full history of the Linux project (1.4 million commits) in only 5.5 GB.
+</p>
+
+<h2> Git is widely used </h2>
+
+<p>
+According to the <a href="https://survey.stackoverflow.co/2022/#version-control-version-control-system-prof">2022 Stack Overflow developer survey</a>,
+96% of professional developers use Git.
+</p>
+
+<h2> Git has a huge ecosystem of tools </h2>
+
+<p>
+The core Git project is just a command-line tool, but Git exploded in popularity
+in the early 2010s thanks to <a href="{{< relurl "tools/hosting">}}">Git hosting services</a>
+like GitLab, GitHub, and more.
+</p>
+
+<p>
+Since Git was created, many
+<a href="{{< relurl "tools/guis" >}}">GUIs</a>, editor integrations,
+and
+<a href="{{< relurl "tools/command-line" >}}">command line tools</a>
+have been built to make working with Git more convenient.
+You favorite developer tools might already have a built-in Git integration.
+</p>
+
+<h2 id="free-and-open-source">Free and Open Source</h2>
+
+<p>
+  Git is released under the <a href="https://opensource.org/licenses/GPL-2.0">
+  GNU General Public License version 2.0</a>, which is an
+  <a href="https://opensource.org/docs/osd">open source license</a>.
+  The Git project chose to use GPLv2 to guarantee your freedom to
+  share and change free software---to make sure the software is
+  free for all its users.
+</p>
+
+<p>
+  However, we do restrict the use of the term "Git" and the
+  <a href="{{< relurl "community/logos" >}}">logos</a> to avoid confusion. Please see our
+  <a href="{{< relurl "about/trademark" >}}">trademark</a> policy for details.
+</p>
+
+
+</div>
+