docs: Mention bug in ALWAYS_SEND_ALL_HOTSPOTS feature.

This should avoid some wasted time.

docs/subsystems/hotspots.md

@@ -46,9 +46,11 @@ However, if you would like to fix the orientation of a hotspot popover, a
 ### Step 3: Test manually
 
 To test your hotspot in the development environment, set
-`ALWAYS_SEND_ALL_HOTSPOTS = True` in `zproject/dev_settings.py`,
-and invoke `hotspots.initialize()` in your browser
-console. Every hotspot should be displayed.
+`ALWAYS_SEND_ALL_HOTSPOTS = True` in `zproject/dev_settings.py`, and
+invoke `hotspots.initialize()` in your browser console. Every hotspot
+should be displayed.  Note that this setting has a bug that can result
+in multiple copies of hotspots appearing; you can clear that by
+reloading the browser.
 
 Here are some visual characteristics to confirm:
 - popover content is readable

zerver/lib/hotspots.py

@@ -1,3 +1,5 @@
+# See https://zulip.readthedocs.io/en/latest/subsystems/hotspots.html
+# for documentation on this subsystem.
 from django.conf import settings
 from django.utils.translation import ugettext as _
 
@@ -36,7 +38,9 @@ ALL_HOTSPOTS = {
 def get_next_hotspots(user: UserProfile) -> List[Dict[str, object]]:
     # For manual testing, it can be convenient to set
     # ALWAYS_SEND_ALL_HOTSPOTS=True in `zproject/dev_settings.py` to
-    # make it easy to click on all of the hotspots.
+    # make it easy to click on all of the hotspots.  Note that
+    # ALWAYS_SEND_ALL_HOTSPOTS has some bugs; see ReadTheDocs (link
+    # above) for details.
     if settings.ALWAYS_SEND_ALL_HOTSPOTS:
         return [{
             'name': hotspot,