Fix broken links in INSTALL.md

CHANGES.md

@@ -1226,7 +1226,10 @@ Crucially, this means __we will not produce .deb packages for Debian 9 (Stretch)
 
 The website https://endoflife.date/ has convenient summaries of the support schedules for projects like [Python](https://endoflife.date/python) and [PostgreSQL](https://endoflife.date/postgresql).
 
-If you are unable to upgrade your environment to a supported version of Python or Postgres, we encourage you to consider using the [Synapse Docker images](./INSTALL.md#docker-images-and-ansible-playbooks) instead.
+If you are unable to upgrade your environment to a supported version of Python or
+Postgres, we encourage you to consider using the
+[Synapse Docker images](https://matrix-org.github.io/synapse/latest/setup/installation.html#docker-images-and-ansible-playbooks)
+instead.
 
 ### Transition Period
 
@@ -1369,11 +1372,11 @@ To upgrade Synapse along with the cryptography package:
 * Administrators using the [`matrix.org` Docker
   image](https://hub.docker.com/r/matrixdotorg/synapse/) or the [Debian/Ubuntu
   packages from
-  `matrix.org`](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#matrixorg-packages)
+  `matrix.org`](https://matrix-org.github.io/synapse/latest/setup/installation.html#matrixorg-packages)
   should ensure that they have version 1.24.0 or 1.23.1 installed: these images include
   the updated packages.
 * Administrators who have [installed Synapse from
-  source](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#installing-from-source)
+  source](https://matrix-org.github.io/synapse/latest/setup/installation.html#installing-from-source)
   should upgrade the cryptography package within their virtualenv by running:
   ```sh
   <path_to_virtualenv>/bin/pip install 'cryptography>=3.3'
@@ -1415,11 +1418,11 @@ To upgrade Synapse along with the cryptography package:
 * Administrators using the [`matrix.org` Docker
   image](https://hub.docker.com/r/matrixdotorg/synapse/) or the [Debian/Ubuntu
   packages from
-  `matrix.org`](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#matrixorg-packages)
+  `matrix.org`](https://matrix-org.github.io/synapse/latest/setup/installation.html#matrixorg-packages)
   should ensure that they have version 1.24.0 or 1.23.1 installed: these images include
   the updated packages.
 * Administrators who have [installed Synapse from
-  source](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#installing-from-source)
+  source](https://matrix-org.github.io/synapse/latest/setup/installation.html#installing-from-source)
   should upgrade the cryptography package within their virtualenv by running:
   ```sh
   <path_to_virtualenv>/bin/pip install 'cryptography>=3.3'
@@ -2998,11 +3001,11 @@ installation remains secure.
 * Administrators using the [`matrix.org` Docker
   image](https://hub.docker.com/r/matrixdotorg/synapse/) or the [Debian/Ubuntu
   packages from
-  `matrix.org`](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#matrixorg-packages)
+  `matrix.org`](https://matrix-org.github.io/synapse/latest/setup/installation.html#matrixorg-packages)
   should ensure that they have version 1.12.0 installed: these images include
   Twisted 20.3.0.
 * Administrators who have [installed Synapse from
-  source](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#installing-from-source)
+  source](https://matrix-org.github.io/synapse/latest/setup/installation.html#installing-from-source)
   should upgrade Twisted within their virtualenv by running:
   ```sh
   <path_to_virtualenv>/bin/pip install 'Twisted>=20.3.0'