docs: Send people to install instructions for latest release.

Pointing these at the latest release, rather than the latest version
in master, allows us to make changes to the installer and document
them properly in master, without making the instructions confusingly
wrong for people who just go to the website or the GitHub repo page
and follow instructions to install.

README.md

@@ -57,7 +57,7 @@ You might be interested in:
 * **Running a Zulip server**. Setting up a server takes just a couple of
   minutes. Zulip runs on Ubuntu 16.04 Xenial and Ubuntu 14.04 Trusty. The
   installation process is
-  [documented here](https://zulip.readthedocs.io/en/latest/production/overview.html).
+  [documented here](https://zulip.readthedocs.io/en/1.7.0/prod.html).
   Commercial support is available; see <https://zulipchat.com/plans> for
   details.
 

templates/zerver/plans.html

@@ -44,7 +44,7 @@
                                     <div class="pricing-details">
                                         Free and open source forever!
                                     </div>
-                                    <a href="https://zulip.readthedocs.io/en/latest/production/overview.html">
+                                    <a href="https://zulip.readthedocs.io/en/1.7.0/prod.html">
                                         <button class="green" type="button">
                                             Install a Zulip server
                                         </button>

version.py

@@ -1,2 +1,6 @@
+# When bumping this for a release, we should also update the handful
+# of places we link to docs for the latest release, rather than master.
+# To find them:   git grep 'zulip.readthedocs.io/en/[0-9]'
 ZULIP_VERSION = "1.7.0+git"
+
 PROVISION_VERSION = '12.0'