docs: document the std.deepJoin function

Fixes #933

Author: johnbartholomew

doc/_stdlib_gen/stdlib-content.jsonnet

@@ -1321,6 +1321,26 @@ local exampleDocMultiline(mid, ex) =
             },
           ],
         },
+        {
+          name: 'deepJoin',
+          params: ['arr'],
+          availableSince: '0.10.0',
+          description: |||
+            Concatenate an array containing strings and arrays to form a single string. If <code>arr</code> is
+            a string, it is returned unchanged. If it is an array, it is flattened and the string elements are
+            concatenated together with no separator.
+          |||,
+          examples: [
+            {
+              input: 'std.deepJoin(["one ", ["two ", "three ", ["four "], []], "five ", ["six"]])',
+              output: std.deepJoin(["one ", ["two ", "three ", ["four "], []], "five ", ["six"]]),
+            },
+            {
+              input: 'std.deepJoin("hello")',
+              output: std.deepJoin("hello")
+            },
+          ],
+        },
         {
           name: 'lines',
           params: ['arr'],

doc/ref/stdlib.html

@@ -2409,6 +2409,40 @@ <h4 id="join">
   </div>
 </div>
 
+<div class="hgroup">
+  <div class="hgroup-inline">
+    <div class="panel">
+      <h4 id="deepJoin">
+        std.deepJoin(arr)
+      </h4>
+    </div>
+    <div style="clear: both"></div>
+  </div>
+</div>
+<div class="hgroup">
+  <div class="hgroup-inline">
+    <div class="panel">
+      <p>
+        <em>
+          Available since version 0.10.0.
+        </em>
+      </p>
+      <p>
+        Concatenate an array containing strings and arrays to form a single string. If <code>arr</code> is
+        a string, it is returned unchanged. If it is an array, it is flattened and the string elements are
+        concatenated together with no separator.
+      </p>
+      <p>
+        Example: <code>std.deepJoin(["one ", ["two ", "three ", ["four "], []], "five ", ["six"]])</code> yields <code>"one two three four five six"</code>.
+      </p>
+      <p>
+        Example: <code>std.deepJoin("hello")</code> yields <code>"hello"</code>.
+      </p>
+    </div>
+    <div style="clear: both"></div>
+  </div>
+</div>
+
 <div class="hgroup">
   <div class="hgroup-inline">
     <div class="panel">