Update dashboard-template-variables rules

We received a GTSE related to Variables (https://new-relic.atlassian.net/browse/NR-265923) which was actually related to documentation.
We want to make sure the usage of uniques and their limits are clear for customers and refer them to the `uniques` documentation if needed.

src/content/docs/query-your-data/explore-query-data/dashboards/dashboard-template-variables.mdx

@@ -321,16 +321,22 @@ As discussed in the [section on defining template variables](#step1), there are
 Note that this is a different topic than writing queries that make use of a template variable.
 </Callout>
 
-Here are some rules and guidance on creating a query-type variable: 
-* Queries must use the `uniques` or `keyset` syntax. Uniques return up to 10,000 results. Check [`uniques`](/docs/query-your-data/nrql-new-relic-query-language/get-started/nrql-syntax-clauses-functions/#func-uniques) and the [`keyset`](/docs/query-your-data/nrql-new-relic-query-language/get-started/nrql-syntax-clauses-functions/#keyset). Here's a couple of query examples: 
+Here are some rules and guidance on creating a query-type variable:
+* Queries must use the `uniques` or `keyset` syntax. 
+* The same syntax and limits of both functions are applicable here. Examples:
 
   ```sql
-  From PageAction select uniques(countryCode)
+  From PageAction select uniques(countryCode)  --> this will return up to 1k results
+  ```
+
+  ```sql
+  From PageAction select uniques(countryCode, 10000) --> this will return up to 10k results
   ```
 
   ```sql
   From PageView select keyset() SINCE 1 day ago
   ```
+Please, check [`uniques`](/docs/nrql/nrql-syntax-clauses-functions/#func-uniques) and the [`keyset`](/docs/nrql/nrql-syntax-clauses-functions/#keyset) for more info.
 
 * You can use almost any NRQL query as long as the `uniques` and `keyset` components return a list of values.
 * Nested variables are not supported: there can't be variables within variables.