man: dockerd: value is optional for --feature flag

The --feature flag allows the boolean value to be omitted.
If only a name is provided, the default is "true".

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

man/dockerd.8.md

@@ -31,7 +31,7 @@ dockerd - Enable daemon mode
 [**--exec-opt**[=*[]*]]
 [**--exec-root**[=*/var/run/docker*]]
 [**--experimental**[=**false**]]
-[**--feature**[=*NAME*=**true**|**false**]
+[**--feature**[=*NAME*[=**true**|**false**]]
 [**--fixed-cidr**[=*FIXED-CIDR*]]
 [**--fixed-cidr-v6**[=*FIXED-CIDR-V6*]]
 [**-G**|**--group**[=*docker*]]
@@ -223,13 +223,13 @@ $ sudo dockerd --add-runtime runc=runc --add-runtime custom=/usr/local/bin/my-ru
 **--experimental**=""
   Enable the daemon experimental features.
 
-**--feature**=*NAME*=**true**|**false**
+**--feature**=*NAME*[=**true**|**false**]
   Enable or disable a feature in the daemon. This option corresponds
   with the "features" field in the daemon.json configuration file. Using
   both the command-line option and the "features" field in the configuration
   file produces an error. The feature option can be specified multiple times
   to configure multiple features.
-  Usage example: `--feature containerd-snapshotter=true`
+  Usage example: `--feature containerd-snapshotter` or `--feature containerd-snapshotter=true`.
 
 **--fixed-cidr**=""
   IPv4 subnet for fixed IPs (e.g., 10.20.0.0/16); this subnet must be nested in