docs: Cross-link root, file_server, php_fastcgi directives (#45)

* docs: Cross-link the `root` directive with file_server/php_fastcgi

* Minor touch-ups

Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>

src/docs/markdown/caddyfile/directives/root.md

@@ -8,6 +8,8 @@ Sets the root path of the site, used by various matchers and directives that acc
 
 Specifically, this directive sets the `{http.vars.root}` placeholder. It is mutually exclusive to other `root` directives in the same block, so it is safe to define multiple roots with matchers that intersect: they will not cascade and overwrite each other.
 
+This directive does not automatically enable serving static files, so it is often used in conjunction with the [`file_server` directive](/docs/caddyfile/directives/file_server) or the [`php_fastcgi` directive](/docs/caddyfile/directives/php_fastcgi).
+
 
 ## Syntax
 
@@ -17,28 +19,35 @@ root [<matcher>] <path>
 
 - **&lt;path&gt;** is the path to use for the site root.
 
-Note that a matcher token is usually required since the first argument is a path, which could look like a path matcher.
+Note that the `<path>` argument could be confused by the parser as a [matcher token](/docs/caddyfile/matchers#syntax) if the it begins with `/`. To disambiguate, specify a wildcard matcher token (`*`). See examples below.
 
 ## Examples
 
 Set the site root to `/home/user/public_html` for all requests:
 
+(Note that a [wildcard matcher](/docs/caddyfile/matchers#wildcard-matchers) is required here because the first argument is ambiguous with a [path matcher](/docs/caddyfile/matchers#path-matchers).)
+
 ```caddy-d
 root * /home/user/public_html
 ```
 
-(A [wildcard matcher](/docs/caddyfile/matchers#wildcard-matchers) is required in this case because the first argument is ambiguous with a [path matcher](/docs/caddyfile/matchers#path-matchers).)
-
 Set the site root to `public_html` (relative to current working directory) for all requests:
 
+(No matcher token is required here because our site root is a relative path, so it does not start with a forward slash and thus is not ambiguous.)
+
 ```caddy-d
 root public_html
 ```
 
-(No matcher token is required here because our site root is a relative path, so it does not start with a forward slash and thus is not ambiguous.)
-
-Set the site root only for requests in `/foo`:
+Change the site root only for requests in `/foo/*`:
 
 ```caddy-d
 root /foo/* /home/user/public_html/foo
 ```
+
+The `root` directive is commonly paired with [`file_server`](/docs/caddyfile/directives/file_server) to serve static files and/or with [`php_fastcgi`](/docs/caddyfile/directives/php_fastcgi) to serve a PHP site:
+
+```caddy-d
+root * /home/user/public_html
+file_server
+```