Add performance issue template

.github/ISSUE_TEMPLATE/bug_report.md

@@ -2,7 +2,7 @@
 name: Bug report
 about: Create a report to help us improve ClickHouse
 title: ''
-labels: bug, issue
+labels: bug
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/performance-issue.md

@@ -0,0 +1,27 @@
+---
+name: Performance issue
+about: Report something working slower than expected
+title: ''
+labels: performance
+assignees: ''
+
+---
+
+(you don't have to strictly follow this form)
+
+**Describe the situation**
+What exactly works slower than expected?
+
+**How to reproduce**
+* Which ClickHouse server version to use
+* Which interface to use, if matters
+* Non-default settings, if any
+* `CREATE TABLE` statements for all tables involved
+* Sample data for all these tables, use [clickhouse-obfuscator](https://github.com/yandex/ClickHouse/blob/master/dbms/programs/obfuscator/Obfuscator.cpp#L42-L80) if necessary
+* Queries to run that lead to slow performance
+
+**Expected performance**
+What are your performance expectation, why do you think they are realistic? Has it been working faster in older ClickHouse releases? Is it working faster in some specific other system?
+
+**Additional context**
+Add any other context about the problem here.