Mention that you need to configure max upload size in reverse proxy as well

changelog.d/10122.doc

@@ -0,0 +1 @@
+Mention in `homeserver.yaml` that you may need to configure max upload size in your reverse proxy. Contributed by @aaronraimist.

docs/sample_config.yaml

@@ -954,6 +954,10 @@ media_store_path: "DATADIR/media_store"
 
 # The largest allowed upload size in bytes
 #
+# If you are using a reverse proxy you will also need to set this value in
+# your reverse proxy's config. See
+# https://matrix-org.github.io/synapse/develop/reverse_proxy.html.
+#
 #max_upload_size: 50M
 
 # Maximum number of pixels that will be thumbnailed

synapse/config/repository.py

@@ -248,6 +248,10 @@ def generate_config_section(self, data_dir_path, **kwargs):
 
         # The largest allowed upload size in bytes
         #
+        # If you are using a reverse proxy you will also need to set this value in
+        # your reverse proxy's config. See
+        # https://matrix-org.github.io/synapse/develop/reverse_proxy.html.
+        #
         #max_upload_size: 50M
 
         # Maximum number of pixels that will be thumbnailed