docs: Remove team member section on homepage in favor of sponsor section

This removes outdated information on the main page in favor of the "official" ways of sponsoring Dokku.

Also update the contributing note to mention where to post

Are you a crypto-user and want other options? Feel free to send bitcoin to 3MY2HxMVsxuWmhQkgYBsE3iZFjJgkjNPyQ

Closes #3374

docs/assets/style.css

@@ -177,7 +177,8 @@ h1 {
 .featurette img {
   width: 400px;
 }
-.slack-channel {
+.slack-channel,
+.sponsors {
   background-color: #EEF1F7;
   font-size: 1.6em;
   font-weight: 300;
@@ -199,28 +200,35 @@ h1 {
 .slack-button img {
   height: 1em;
 }
-.team-members img {
-  -moz-box-shadow: 4px 4px 8px 0px rgba(0,0,0,0.75);
-  -webkit-border-radius: 3px;
-  -webkit-box-shadow: 4px 4px 8px 0px rgba(0,0,0,0.75);
-  border-radius: 3px;
-  border: 8px solid white;
-  box-shadow: 4px 4px 8px 0px rgba(0,0,0,0.75);
-  display: block;
-  height: 200px;
-  margin: 20px auto 20px auto;
+.sponsors {
+  background-color: #272822;
+  color: #FCFCFC;
 }
-.team-members .fund-link {
+.sponsors a {
+  color: #f0ad4e;
+}
+.sponsors .backer img,
+.sponsors .sponsor img {
+  -webkit-border-radius: 3px;
+  border-radius: 3px;
+  border: 8px solid gray;
+  margin: 20px auto 20px auto;
+  max-width: 192px;
+}
+.sponsors .backer img {
+  -webkit-border-radius: 50%;
+  border-radius: 50%;
+  border: 0;
+}
+.sponsors img:hover {
+  -moz-box-shadow: 4px 4px 8px 0px rgba(0,0,0,0.75);
+  -webkit-box-shadow: 4px 4px 8px 0px rgba(0,0,0,0.75);
+  box-shadow: 0px 0px 32px 0px rgba(0,0,0,0.75);
+}
+.sponsors .fund-link {
   display: block;
   font-size: .8em;
 }
-.team-member {
-  min-height: 320px;
-}
-.team-member-image img:last-child { display: none }
-.team-member-image:hover img:first-child { display: none; }
-.team-member-image:hover img:last-child { display: inline-block; }
-
 .list-group-item {
   border: none;
   font-size: 1.1em;