Merge pull request #355 from tracim/fix/201/ldap_documentation

doc/setting.md

 
 ## LDAP ##
 
-To use LDAP authentication, set `auth_type` parameter to `ldap`:
+`Tracim` is able to authenticate users via `LDAP`. To enable this feature, start by setting the authentication type as follow:
 
     auth_type = ldap
 
-Then add LDAP parameters
+Then add these `LDAP` parameters:
 
     # LDAP server address
     ldap_url = ldap://localhost:389