Once you have the module enabled, you just need you just need the following changes to your httpd.conf file:
1) Enable the mod if it isn't enabled already
LoadModule substitute_module modules/mod_substitute.so
2) Configure the module to add the script tag to all html pages
AddOutputFilterByType SUBSTITUTE text/html
Substitute "s|<head>|<head><script src='https://jsagent.tcell.io/tcellagent.min.js' tcellappid='ADD_APP_ID' tcellapikey='ADD_API_KEY'></script>|niq"
Note: You can get your app ID and API key from the tcell management console as described here.