Add support for tab completion (#12411)

* Add support for tab completion

* make flake8 happy

* Add documentation

docs/_summary.md

@@ -29,6 +29,7 @@
     * [Overview](cli.md)
     * [Configuration](cli_configuration.md)
     * [Commands](cli_commands.md)
+    * [Tab Completion](cli_tab_complete.md)
 
 * Using QMK
   * Guides

docs/cli_tab_complete.md

@@ -0,0 +1,27 @@
+# Tab Completion for QMK
+
+If you are using Bash 4.2 or later, Zsh, or FiSH you can enable Tab Completion for the QMK CLI. This will let you tab complete the names of flags, keyboards, files, and other `qmk` options.
+
+## Setup
+
+There are several ways you can setup tab completion.
+
+### For Your User Only
+
+Add this to the end of your `.profile` or `.bashrc`:
+
+    source ~/qmk_firmware/util/qmk_tab_complete.sh
+
+If you put `qmk_firmware` into another location you will need to adjust this path.
+
+### System Wide Symlink
+
+If you want the tab completion available to all users of the system you can add a symlink to the `qmk_tab_complete.sh` script:
+
+    `ln -s ~/qmk_firmware/util/qmk_tab_complete.sh /etc/profile.d/qmk_tab_complete.sh`
+
+### System Wide Copy
+
+In some cases a symlink may not work. Instead you can copy the file directly into place. Be aware that updates to the tab complete script may happen from time to time, you will want to recopy the file periodically.
+
+    cp util/qmk_tab_complete.sh /etc/profile.d