Rename some "python3" symbols to "py3", as the command name.
Documentation updates.
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index 6a4839b..069154a 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1382,6 +1382,8 @@
|:ptselect| :pts[elect] |:tselect| and show tag in preview window
|:put| :pu[t] insert contents of register in the text
|:pwd| :pw[d] print current directory
+|:py3| :py3 execute Python 3 command
+|:p3yfile| :py3f[ile] execute Python 3 script file
|:python| :py[thon] execute Python command
|:pyfile| :pyf[ile] execute Python script file
|:quit| :q[uit] quit current window (when one window quit Vim)