make sure user doesn't accidentally put their credentials in git

.gitignore

@@ -1,6 +1,7 @@
 .pio
 main/configuration.h
 main/credentials.h
+credentials-private.h
 
 # ignore vscode IDE settings files
 .vscode/*
@@ -8,4 +9,4 @@ main/credentials.h
 !.vscode/tasks.json
 !.vscode/launch.json
 !.vscode/extensions.json
-*.code-workspace
+*.code-workspace