Update vim/xdebug.md

vim/xdebug.md

@@ -20,13 +20,27 @@ xdebug.client_host=localhost
 xdebug.client_port=9003
 xdebug.idekey="NVIM"
 xdebug.log=/tmp/xdebug.log
+
+; always initiate a debugging session
 xdebug.start_with_request=yes
+
+; activates if a "trigger" is present
 ;xdebug.start_with_request=trigger
 ```
 
+To signal the debugger to initiate connections, Xdebug will look whether the XDEBUG_SESSION environment variable is present.
+
+```
+export XDEBUG_SESSION=1
+```
 
 ### Test
 
 ```sh
 php --info
 ```
+
+
+### debug
+
+- port 9003 must not been blocked