run: create -F option to run base64 encoded command after busybox init

Fix ./run -h which was showing the build help instead.

run-usage.adoc

@@ -19,6 +19,8 @@
                       Only options that come before the `-`, i.e. "standard"
                       options, should be passed with this option.
                       Example: `./run -a arm -e 'init=/poweroff.out'`
+|`-F` |`CMDSTR`      |Much like `-f`, but base64 encods the string.
+                      Mnemonic: `-F` is to `-f` what `-E` is to `-e`.
 |`-f` |`CLI_OPTIONS` |Pass an extra Linux kernel command line options,
                       add a dash `-` separator, and place the options after the dash.
                       Intended for custom options understood by our `init` scripts,