doc: update build instructions

- add missing dependencies
- remove redundant "Install dependencies" section

Change-Id: I930e73f2d4aa3c2c4e94b09ba71889cbe2b3d2ac
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4297437..d4ffb09 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,9 +22,9 @@
 option(DHTNET_NATPMP "Enable NAT-PMP support" ON)
 option(DHTNET_TESTABLE "Enable API for tests" ON)
 option(BUILD_TOOLS "Build tools" ON)
-option(BUILD_BENCHMARKS "Build benchamrks" ON)
+option(BUILD_BENCHMARKS "Build benchmarks" ON)
 option(BUILD_DEPENDENCIES "Build dependencies" ON)
-option (DNC_SYSTEMD_UNIT_FILE_LOCATION "Where to install systemd unit file")
+option(DNC_SYSTEMD_UNIT_FILE_LOCATION "Where to install systemd unit file")
 option(DNC_SYSTEMD "Enable dnc systemd integration" ON)
 option(CODE_COVERAGE "Enable coverage reporting" OFF)
 
@@ -195,6 +195,7 @@
         message("libupnp not found: disabling")
         set(DHTNET_PUPNP Off)
     else()
+        message("libupnp found")
         set(upnp_LIBRARIES PkgConfig::upnp)
         set (requiresprivate "${requiresprivate} libupnp")
     endif()