fix heading levels

tsa/howto/conference.mdwn

@@ -56,9 +56,9 @@ started looking into
 
 ## Alternatives considered
 
-## mumble
+### mumble
 
-### features
+#### features
 
  * audio-only
  * moderation
@@ -68,7 +68,7 @@ started looking into
  * chat
  * dial-in, unmaintained, might be broken: https://github.com/slomkowski/mumsi
 
-### installation
+#### installation
 
 there are two different puppet modules to setup mumble:
 
@@ -78,9 +78,9 @@ there are two different puppet modules to setup mumble:
 still need to be evaluated, but i'd be tempted to use the voxpupuli
 module because they tend to be better tested and it's more recent
 
-## jitsi
+### jitsi
 
-### installation
+#### installation
 
 ansible roles: https://code.immerda.ch/o/ansible-jitsi-meet/ https://github.com/UdelaRInterior/ansible-role-jitsi-meet
 
@@ -90,13 +90,13 @@ there's also a docker container and (messy) debian packages
 
 prometheus exporter: https://github.com/systemli/prometheus-jitsi-meet-exporter
 
-## Nextcloud Talk
+### Nextcloud Talk
 
 systemli is using this ansible role to install coturn: https://github.com/systemli/ansible-role-coturn
 
-## BBB
+### BBB
 
-### features
+#### features
 
  * audio, video conferencing support
  * [accesssible](http://docs.bigbluebutton.org/support/faq.html#accessibility) with live closed captionning and support for screen readers
@@ -109,7 +109,7 @@ systemli is using this ansible role to install coturn: https://github.com/system
 
 i tested an instance setup by a fellow sysadmin and we had trouble after a while, even with two people, doing a screenshare. it's unclear what the cause of the problem was: maybe the server was overloaded. more testing required.
 
-### installation
+#### installation
 
 [based on unofficial Debian packages](https://docs.bigbluebutton.org/2.2/install.html), requires Freeswitch for
 dialin, which doesn't behave well under virtualization (so would need