document limits on using dots in service names

Fixes #1205

README.md

@@ -981,6 +981,9 @@ This will returns services which are deemed "passing" or "warning" according to
 their node and service-level checks defined in Consul. Please note that the
 comma implies an "or", not an "and".
 
+**Note:** Due to the use of dot `.` to delimit TAG, the `service` command will
+not recognize service names containing dots.
+
 **Note:** There is an architectural difference between the following:
 
 ```liquid
@@ -994,6 +997,7 @@ and perform client-side filtering. As a general rule, do not use the "passing"
 argument alone if you want only healthy services - simply omit the second
 argument instead.
 
+
 ##### `services`
 
 Query [Consul][consul] for all services in the catalog.
@@ -1862,6 +1866,14 @@ func main() {
 
 ## Caveats
 
+### Dots in Service Names
+
+Using dots `.` in service names will conflict with the use of dots for [TAG
+delineation](https://github.com/hashicorp/consul-template#service) in the
+template. Dots already [interfere with using
+DNS](https://www.consul.io/docs/agent/services.html#service-and-tag-names-with-dns)
+for service names, so we recommend avoiding dots wherever possible.
+
 ### Once Mode
 
 In Once mode, Consul Template will wait for all dependencies to be rendered. If