Add apex help_content for certs,nginx,storage,tar plugins

Also corrects some punctuation in associated help_content.

plugins/certs/commands

@@ -7,13 +7,14 @@ case "$1" in
     help_content_func () {
       declare desc="return certs plugin help content"
       cat<<help_content
+    certs, Manage Dokku apps SSL (TLS) certs
     certs:add <app> CRT KEY, Add an ssl endpoint to an app. Can also import from a tarball on stdin
-    certs:chain CRT [CRT ...], [NOT IMPLEMENTED] Print the ordered and complete chain for the given certificate.
+    certs:chain CRT [CRT ...], [NOT IMPLEMENTED] Print the ordered and complete chain for the given certificate
     certs:generate <app> DOMAIN, Generate a key and certificate signing request (and self-signed certificate)
-    certs:info <app>, Show certificate information for an ssl endpoint.
-    certs:key <app> CRT KEY [KEY ...], [NOT IMPLEMENTED] Print the correct key for the given certificate.
-    certs:remove <app>, Remove an SSL Endpoint from an app.
-    certs:rollback <app>, [NOT IMPLEMENTED] Rollback an SSL Endpoint for an app.
+    certs:info <app>, Show certificate information for an ssl endpoint
+    certs:key <app> CRT KEY [KEY ...], [NOT IMPLEMENTED] Print the correct key for the given certificate
+    certs:remove <app>, Remove an SSL Endpoint from an app
+    certs:rollback <app>, [NOT IMPLEMENTED] Rollback an SSL Endpoint for an app
     certs:update <app> CRT KEY, Update an SSL Endpoint on an app. Can also import from a tarball on stdin
 help_content
     }

plugins/nginx-vhosts/commands

@@ -7,6 +7,7 @@ case "$1" in
     help_content_func () {
       declare desc="return nginx plugin help content"
       cat<<help_content
+    nignx, Interact with Dokku's Nginx proxy
     nginx:build-config <app>, (Re)builds nginx config for given app
     nginx:access-logs <app> [-t], Show the nginx access logs for an application (-t follows)
     nginx:error-logs <app> [-t], Show the nginx error logs for an application (-t follows)
@@ -16,7 +17,7 @@ help_content
     if [[ $1 = "nginx:help" ]] ; then
         echo -e 'Usage: dokku nginx[:COMMAND]'
         echo ''
-        echo 'Interact with Dokkus Nginx proxy.'
+        echo 'Interact with Dokku'"'"'s Nginx proxy.'
         echo ''
         echo 'Additional commands:'
         help_content_func | sort | column -c2 -t -s,

plugins/storage/commands

@@ -7,6 +7,7 @@ case "$1" in
     help_content_func () {
       declare desc="return storage plugin help content"
       cat<<help_content
+    storage, Mount local volume / directories inside containers
     storage:list <app>, List bind mounts for app's container(s) (host:container)
     storage:mount <app> <host-dir:container-dir>, Create a new bind mount
     storage:unmount <app> <host-dir:container-dir>, Remove an existing bind mount

plugins/tar/commands

@@ -7,8 +7,9 @@ case "$1" in
     help_content_func () {
       declare desc="return tar plugin help content"
       cat<<help_content
+    tar, An alternative to using git. Apps are loaded via tarballs instead
     tar:in <app>, Reads an tarball containing the app from stdin
-    tar:from <app> <url>, Loads an app tarball from url.
+    tar:from <app> <url>, Loads an app tarball from url
 help_content
     }