Add docs for --dns-search=.

PR 6720 introduce that use `--dns-search=.` will not set `search` in `/etc/resolv.conf`.

Signed-off-by: Huayi Zhang <irachex@gmail.com>

docs/man/docker-create.1.md

@@ -64,7 +64,7 @@ docker-create - Create a new container
    Add a host device to the container (e.g. --device=/dev/sdc:/dev/xvdc:rwm)
 
 **--dns-search**=[]
-   Set custom DNS search domains
+   Set custom DNS search domains (Use --dns-search=. if you don't wish to set the search domain)
 
 **--dns**=[]
    Set custom DNS servers

docs/man/docker-run.1.md

@@ -103,7 +103,7 @@ stopping the process by pressing the keys CTRL-P CTRL-Q.
    Add a host device to the container (e.g. --device=/dev/sdc:/dev/xvdc:rwm)
 
 **--dns-search**=[]
-   Set custom DNS search domains
+   Set custom DNS search domains (Use --dns-search=. if you don't wish to set the search domain)
 
 **--dns**=*IP-address*
    Set custom DNS servers. This option can be used to override the DNS

docs/sources/articles/networking.md

@@ -170,6 +170,7 @@ Four different options affect container domain name services.
     When a container process attempts to access `host` and the search
     domain `example.com` is set, for instance, the DNS logic will not
     only look up `host` but also `host.example.com`.
+    Use `--dns-search=.` if you don't wish to set the search domain.
 
 Note that Docker, in the absence of either of the last two options
 above, will make `/etc/resolv.conf` inside of each container look like

docs/sources/reference/commandline/cli.md

@@ -1191,7 +1191,7 @@ removed before the image is removed.
       -d, --detach=false         Detached mode: run the container in the background and print the new container ID
       --device=[]                Add a host device to the container (e.g. --device=/dev/sdc:/dev/xvdc:rwm)
       --dns=[]                   Set custom DNS servers
-      --dns-search=[]            Set custom DNS search domains
+      --dns-search=[]            Set custom DNS search domains (Use --dns-search=. if you don't wish to set the search domain)
       -e, --env=[]               Set environment variables
       --entrypoint=""            Overwrite the default ENTRYPOINT of the image
       --env-file=[]              Read in a line delimited file of environment variables