docs: Add semver link and note on empty string format to deprecate doc (#68)

PR-URL: #68
Credit: @neverett
Reviewed-By: @zkat

Author: neverett

doc/cli/npm-deprecate.md

@@ -10,15 +10,17 @@ npm-deprecate(1) -- Deprecate a version of a package
 This command will update the npm registry entry for a package, providing
 a deprecation warning to all who attempt to install it.
 
-It works on version ranges as well as specific versions, so you can do
-something like this:
+It works on [version ranges](https://semver.npmjs.com/) as well as specific 
+versions, so you can do something like this:
 
     npm deprecate my-thing@"< 0.2.3" "critical bug fixed in v0.2.3"
 
 Note that you must be the package owner to deprecate something.  See the
 `owner` and `adduser` help topics.
 
-To un-deprecate a package, specify an empty string (`""`) for the `message` argument.
+To un-deprecate a package, specify an empty string (`""`) for the `message` 
+argument. Note that you must use double quotes with no space between them to 
+format an empty string.
 
 ## SEE ALSO