scan-tree: Support gitweb.category.

Use gitweb.category from git config to determine repo's section, if
option is enabled.

cgitrc.5.txt

@@ -118,6 +118,12 @@ enable-gitweb-owner::
 	for the git config value "gitweb.owner" to determine the owner.
 	Default value: "1". See also: scan-path.
 
+enable-gitweb-section::
+	If set to "1" and scan-path is enabled, we first check each repository
+	for the git config value "gitweb.category" to determine the repository's
+	section. This value is overridden if section-from-path is enabled.
+	Default value: "1". See also: scan-path section-from-path.
+
 enable-http-clone::
 	If set to "1", cgit will act as an dumb HTTP endpoint for git clones.
 	If you use an alternate way of serving git repositories, you may wish