Improve the maintenance badge user experience

* Change the alt-text to be a little more descriptive
  and screen-reader friendly
* Link to the Cargo documentation from the badge which describes what
  the maintenance intentions are

Author: jhinch

app/components/badge-maintenance.hbs

@@ -1,9 +1,11 @@
 <span class="badge" ...attributes>
   {{#unless this.none}}
-    <img
-        src="https://img.shields.io/badge/maintenance-{{this.escapedStatus}}-{{this.color}}.svg"
-        alt="{{this.text}}"
-        title="{{this.text}}">
+    <a href="https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata">
+      <img
+          src="https://img.shields.io/badge/maintenance-{{this.escapedStatus}}-{{this.color}}.svg"
+          alt="{{this.text}}"
+          title="{{this.text}}">
+    </a>
   {{/unless}}
 
 </span>

app/components/badge-maintenance.js

@@ -33,5 +33,21 @@ export default Component.extend({
     }
   }),
 
-  text: 'Maintenance intention for this crate',
+  // eslint-disable-next-line ember/require-return-from-computed
+  text: computed('badge', function() {
+    switch (this.get('badge.attributes.status')) {
+      case 'actively-developed':
+        return 'Maintenance intention: Actively developed';
+      case 'passively-maintained':
+        return 'Maintenance intention: Passively maintained';
+      case 'as-is':
+        return 'Maintenance intention: As-is';
+      case 'experimental':
+        return 'Maintenance intention: Experimental';
+      case 'looking-for-maintainer':
+        return 'Maintenance intention: Looking for maintainer';
+      case 'deprecated':
+        return 'Maintenance intention: Deprecated';
+    }
+  }),
 });

app/templates/maintenance-intentions.hbs

@@ -0,0 +1,51 @@
+{{ title 'Maintenance intention guidelines' }}
+<div id='crates-heading'>
+  {{svg-jar 'circle-with-i'}}
+  <h1>Maintenance intention guidelines</h1>
+</div>
+
+<p>
+  The maintenance badge is a way for crate maintainers to convey their
+  maintenance intentions. The definitions below provide a high level
+  categorization. The exact cadence for releases or support provided
+  will still vary between crates. Crate maintainers should provide
+  further details in their crate's documentation if they wish to
+  clarify their intentions or commitments. Crate maintainers should
+  refer to the <a href="https://doc.rust-lang.org/cargo/reference/manifest.html">Cargo manifest documentation</a>
+  for more information on how to add a maintenance badge.
+</p>
+
+<h2>Categories</h2>
+
+<dl id='maintenance-intentions'>
+  <dt>Actively developed<BadgeMaintenance @badge={{hash attributes=(hash status="actively-developed")}} /></dt>
+  <dd>
+    New features are being added and bugs are being fixed.
+  </dd>
+  <dt>Passively maintained<BadgeMaintenance @badge={{hash attributes=(hash status="passively-maintained")}} /></dt>
+  <dd>
+    There are no plans for new features, but the maintainer intends to respond
+    to issues that get filed.
+  </dd>
+  <dt>As-is<BadgeMaintenance @badge={{hash attributes=(hash status="as-is")}} /></dt>
+  <dd>
+    The crate is feature complete, the maintainer does not intend to continue
+    working on it or providing support, but it works for the purposes it was
+    designed for.
+  </dd>
+  <dt>Experimental<BadgeMaintenance @badge={{hash attributes=(hash status="experimental")}} /></dt>
+  <dd>
+    The author wants to share it with the community but is not intending to meet
+    anyone's particular use case.
+  </dd>
+  <dt>Looking for maintainer<BadgeMaintenance @badge={{hash attributes=(hash status="looking-for-maintainer")}} /></dt>
+  <dd>
+    The current maintainer would like to transfer the crate to someone else.
+  </dd>
+  <dt>Deprecated<BadgeMaintenance @badge={{hash attributes=(hash status="deprecated")}} /></dt>
+  <dd>
+    The maintainer does not recommend using this crate, possibly due there being
+    a better solution available or being problems with the crate that they
+    do not want to fix.
+  </dd>
+</dl>