Add CLI command for flashing a keyboard

A new CLI subcommand was added, flash, which behaves very similar to the already present compile CLI comamnd, but with the added ability to target a bootloader. The command is used like so: qmk flash [-h] [-b] [-kb KEYBOARD] [-km KEYMAP] [-bl BOOTLOADER] [filename].

A -kb <keyboard> and -km <keymap> is expected, or a configurator export JSON filename. A bootloader can be specified using -bl <target>, and if left unspecified, the target is assumed to be :flash. -bl can be used to list the available bootloaders.

If -km <keymap> is provided, but no -kb <keyboard>, then a message is printed suggesting the user to run qmk list_keyboards.

1 files changed, 24 insertions, 0 deletions

diff --git a/docs/cli.md b/docs/cli.md
index fb7d17d2a1..1c09527221 100644
--- a/docs/cli.md
+++ b/docs/cli.md
@@ -95,6 +95,30 @@ qmk compile <configuratorExport.json>
 qmk compile -kb <keyboard_name> -km <keymap_name>
 ```
 
+## `qmk flash`
+
+This command is similar to `qmk compile`, but can also target a bootloader. The bootloader is optional, and is set to `:flash` by default.
+To specify a different bootloader, use `-bl <bootloader>`. Visit <https://docs.qmk.fm/#/flashing>
+for more details of the available bootloaders.
+
+**Usage for Configurator Exports**:
+
+```
+qmk flash <configuratorExport.json> -bl <bootloader>
+```
+
+**Usage for Keymaps**:
+
+```
+qmk flash -kb <keyboard_name> -km <keymap_name> -bl <bootloader>
+```
+
+**Listing the Bootloaders**
+
+```
+qmk flash -b
+```
+
 ## `qmk config`
 
 This command lets you configure the behavior of QMK. For the full `qmk config` documentation see [CLI Configuration](cli_configuration.md).