Add README for testserver

Author: ZhouXing19

testserver/README.md

@@ -0,0 +1,66 @@
+# cockroach-go Testserver
+
+The `testserver` package helps running cockroachDB binary with tests. It 
+automatically downloads the latest stable cockroach binary for your runtimeOS 
+(Linux-amd64 and Darwin-amd64 only for now), or attempts to run "cockroach" from your PATH.
+
+### Example
+To run the test server, call `NewTestServer(opts)` and with test server options. 
+
+Here's an example of starting a test server without server options (i.e. in `Insecure` 
+mode).
+
+```go
+  import "github.com/cockroachdb/cockroach-go/v2/testserver"
+  import "testing"
+  import "time"
+
+  func TestRunServer(t *testing.T) {
+     ts, err := testserver.NewTestServer()
+     if err != nil {
+       t.Fatal(err)
+     }
+     defer ts.Stop()
+
+     db, err := sql.Open("postgres", ts.PGURL().String())
+     if err != nil {
+       t.Fatal(err)
+     }
+   }
+```
+
+**Note: please always use `testserver.NewTestServer()` to start a test server. Never use 
+`testserver.Start()`.**
+
+### Test Server Options
+
+The default configuration is :
+
+- in insecure mode, so not using TLS certificates to encrypt network;
+- storing data to memory, with 20% of hard drive space assigned to the node;
+- auto-downloading the latest stable release of cockroachDB.
+
+You can also choose from the following options and pass them to `testserver.
+NewTestServer()`.
+
+- **Secure Mode**: run a secure multi-node cluster locally, using TLS certificates to encrypt network communication.
+    See also https://www.cockroachlabs.com/docs/stable/secure-a-cluster.html.
+  - Usage: ```NewTestServer(testserver.SecureOpt())```
+- **Set Root User's Password**: set the given password for the root user for the
+  PostgreSQL server, so to avoid having to use client certificates. This option can 
+  only be passed under secure mode. 
+  - Usage: ```NewTestServer(testserver.RootPasswordOpt
+    (your_password))```
+- **Store On Disk**: store the database to the local disk. By default, the database is 
+  saved at `/tmp/cockroach-testserverxxxxxxxx`, with randomly generated `xxxxxxxx` 
+  postfix. 
+  - Usage: ```NewTestServer(testserver.StoreOnDiskOpt())```
+- **Set Memory Allocation for Databse Storage**: set the maximum percentage of 
+  total memory space assigned to store the database. 
+  See also https://www.cockroachlabs. com/docs/stable/cockroach-start.html. 
+  - Usage: 
+    ```NewTestServer(testserver.SetStoreMemSizeOpt(0.3))```
+
+### Test Server for Multi Tenants
+The usage of test server as a tenant server is still under development. Please 
+check `testserver/tenant.go` for more information.