docs(csgo): set clientappid in common.cfg and document the mod install order

[borzaka]

Description

Follow-up to the CS:GO client App ID section (GameServerManagers/LinuxGSM#4963), and fixes some inaccuracies from #126

• Recommend setting clientappid in common.cfg instead of the instance config, as it writes to files shared by all instances using the same serverfiles. This applies to both the "Client App ID" section and the upgrade notes.
• Mention that steam.inf is overwritten too, not only steam_appid.txt, when instances with different values share serverfiles.
• Clarify the mod install steps: run mods-install three times (metamodsource, sourcemod, nolobbyreservation), and NoLobbyReservation can only be installed after SourceMod.
• NoLobbyReservation is compiled during both mods-install and mods-update.
• The upgrade note for standalone CS:GO players now lists all three mods and links to the NoLobbyReservation section.