docs: Update global links to new contributing guide URL.

Logically, these are part of the previous commit, but won't pass CI
until ReadTheDocs has built the previous commit and generated the
target page.

README.md

@@ -33,16 +33,16 @@ Come find us on the [development community chat](https://zulip.com/development-c
 ## Getting started
 
 - **Contributing code**. Check out our [guide for new
-  contributors](https://zulip.readthedocs.io/en/latest/overview/contributing.html)
+  contributors](https://zulip.readthedocs.io/en/latest/contributing/contributing.html)
   to get started. We have invested into making Zulip’s code uniquely readable,
   well tested, and easy to modify. Beyond that, we have written an extraordinary
   150K words of documentation on how to contribute to Zulip.
 
 - **Contributing non-code**. [Report an
-  issue](https://zulip.readthedocs.io/en/latest/overview/contributing.html#reporting-issues),
+  issue](https://zulip.readthedocs.io/en/latest/contributing/contributing.html#reporting-issues),
   [translate](https://zulip.readthedocs.io/en/latest/translating/translating.html)
   Zulip into your language, or [give us
-  feedback](https://zulip.readthedocs.io/en/latest/overview/contributing.html#user-feedback).
+  feedback](https://zulip.readthedocs.io/en/latest/contributing/contributing.html#user-feedback).
   We'd love to hear from you, whether you've been using Zulip for years, or are just
   trying it out for the first time.
 
@@ -64,14 +64,14 @@ Come find us on the [development community chat](https://zulip.com/development-c
   projects](https://zulip.com/for/open-source/).
 
 - **Participating in [outreach
-  programs](https://zulip.readthedocs.io/en/latest/overview/contributing.html#outreach-programs)**
+  programs](https://zulip.readthedocs.io/en/latest/contributing/contributing.html#outreach-programs)**
   like [Google Summer of Code](https://developers.google.com/open-source/gsoc/)
   and [Outreachy](https://www.outreachy.org/).
 
 - **Supporting Zulip**. Advocate for your organization to use Zulip, become a
   [sponsor](https://github.com/sponsors/zulip), write a review in the mobile app
   stores, or [help others find
-  Zulip](https://zulip.readthedocs.io/en/latest/overview/contributing.html#help-others-find-zulip).
+  Zulip](https://zulip.readthedocs.io/en/latest/contributing/contributing.html#help-others-find-zulip).
 
 You may also be interested in reading our [blog](https://blog.zulip.org/), and
 following us on [Twitter](https://twitter.com/zulip) and

frontend_tests/node_tests/copy_and_paste.js

@@ -59,10 +59,10 @@ run_test("paste_handler", () => {
     );
 
     input =
-        '<meta http-equiv="content-type" content="text/html; charset=utf-8"><a class="reference external" href="https://zulip.readthedocs.io/en/latest/overview/contributing.html" style="box-sizing: border-box; color: hsl(283, 39%, 53%); text-decoration: none; cursor: pointer; outline: 0px; font-family: Lato, proxima-nova, &quot;Helvetica Neue&quot;, Arial, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: hsl(0, 0%, 99%);">Contributing to Zulip</a>';
+        '<meta http-equiv="content-type" content="text/html; charset=utf-8"><a class="reference external" href="https://zulip.readthedocs.io/en/latest/contributing/contributing.html" style="box-sizing: border-box; color: hsl(283, 39%, 53%); text-decoration: none; cursor: pointer; outline: 0px; font-family: Lato, proxima-nova, &quot;Helvetica Neue&quot;, Arial, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: hsl(0, 0%, 99%);">Contributing guide</a>';
     assert.equal(
         copy_and_paste.paste_handler_converter(input),
-        "[Contributing to Zulip](https://zulip.readthedocs.io/en/latest/overview/contributing.html)",
+        "[Contributing guide](https://zulip.readthedocs.io/en/latest/contributing/contributing.html)",
     );
 
     input =

templates/zerver/footer.html

@@ -128,8 +128,8 @@
         <ul>
             <li><a href="https://github.com/zulip/zulip/">{{ _("GitHub") }}</a></li>
             <li>
-                <a href="https://zulip.readthedocs.io/en/latest/overview/contributing.html">
-                    {{ _("Contributing to Zulip") }}
+                <a href="https://zulip.readthedocs.io/en/latest/contributing/contributing.html">
+                    {{ _("Contributing guide") }}
                 </a>
             </li>
             <li><a href="/development-community/">{{ _("Development community") }}</a></li>