[rubygems/rubygems] Add default_cli_command documentation

I suspect most experienced users won't like the change in defaults, so
document the setting to toggle back the current default.

ruby/rubygems@93e2e2bef9

Author: deivid-rodriguez

lib/bundler/man/bundle-config.1

@@ -77,6 +77,9 @@ Whether Bundler should run \fBbundle clean\fR automatically after \fBbundle inst
 \fBconsole\fR (\fBBUNDLE_CONSOLE\fR)
 The console that \fBbundle console\fR starts\. Defaults to \fBirb\fR\.
 .TP
+\fBdefault_cli_command\fR (\fBBUNDLE_DEFAULT_CLI_COMMAND\fR)
+The command that running \fBbundle\fR without arguments should run\. Defaults to \fBcli_help\fR since Bundler 4, but can also be \fBinstall\fR which was the previous default\.
+.TP
 \fBdeployment\fR (\fBBUNDLE_DEPLOYMENT\fR)
 Equivalent to setting \fBfrozen\fR to \fBtrue\fR and \fBpath\fR to \fBvendor/bundle\fR\.
 .TP

lib/bundler/man/bundle-config.1.ronn

@@ -99,6 +99,10 @@ learn more about their operation in [bundle install(1)](bundle-install.1.html).
    explicitly configured.
 * `console` (`BUNDLE_CONSOLE`):
    The console that `bundle console` starts. Defaults to `irb`.
+* `default_cli_command` (`BUNDLE_DEFAULT_CLI_COMMAND`):
+   The command that running `bundle` without arguments should run. Defaults to
+   `cli_help` since Bundler 4, but can also be `install` which was the previous
+   default.
 * `deployment` (`BUNDLE_DEPLOYMENT`):
    Equivalent to setting `frozen` to `true` and `path` to `vendor/bundle`.
 * `disable_checksum_validation` (`BUNDLE_DISABLE_CHECKSUM_VALIDATION`):