docs: lsp, ui events, dev guidance, osc7

fix #34981

runtime/lua/vim/_system.lua

@@ -471,6 +471,10 @@ end
 
 --- Runs a system command or throws an error if {cmd} cannot be run.
 ---
+--- The command runs directly (not in 'shell') so shell builtins such as "echo" in cmd.exe, cmdlets
+--- in powershell, or "help" in bash, will not work unless you actually invoke a shell:
+--- `vim.system({'bash', '-c', 'help'})`.
+---
 --- Examples:
 ---
 --- ```lua