doc/manuals: Fix title out of sequence

asciidoc: WARNING: install.adoc: line 450: section title out of sequence: expected level 3, got level 4

Change-Id: I0c881405e66cc6815533bb884016db20cfdff3dc
diff --git a/doc/manuals/chapters/install.adoc b/doc/manuals/chapters/install.adoc
index e062b8d..30db8be 100644
--- a/doc/manuals/chapters/install.adoc
+++ b/doc/manuals/chapters/install.adoc
@@ -447,7 +447,7 @@
 is required here.
 
 [[install_capture_packets]]
-===== Capture Packets
+==== Capture Packets
 
 In order to allow collecting pcap traces of the network communication for later
 reference, allow the osmo-gsm-tester group to capture packets using the 'tcpdump'
@@ -488,7 +488,7 @@
 your terminal is in turn is picked up in the tcpdump trace, and so forth. When
 testing 'tcpdump' access, make sure to have proper filter expressions in place.
 
-===== Allow Core Files
+==== Allow Core Files
 
 In case a binary run for the test crashes, a core file of the crash should be
 written. This requires a limit rule. Create a file with the required rule:
@@ -512,7 +512,7 @@
 under 'osmo-gsm-tester.git/utils/limits.d/', so one can simply cp them from
 there.
 
-===== Allow Realtime Priority
+==== Allow Realtime Priority
 
 Certain binaries should be run with real-time priority, like 'osmo-bts-trx'.
 Add this permission on the main unit:
@@ -567,7 +567,7 @@
 there.
 
 [[user_config_uhd]]
-===== UHD
+==== UHD
 
 Grant permission to use the UHD driver to run USRP devices for osmo-bts-trx, by
 adding the jenkins user to the 'usrp' group: