update design doc to cover the examples of setting multiple failpoints

Signed-off-by: Benjamin Wang <[email protected]>

doc/design.md

@@ -48,6 +48,11 @@ The static way is to set [gofail terms](#gofail-term) using environment variable
 $ GOFAIL_FAILPOINTS='my/package/path/SomeFuncString=sleep("600s")' ./cmd
 ```
 
+You can set multiple failpoints by using ";" as the delimiter,
+```
+GOFAIL_FAILPOINTS='failpoint1=return("hello");failpoint2=sleep(10)' ./cmd
+```
+
 The dynamic way is to set an HTTP endpoint using environment variable `GOFAIL_HTTP` when starting your application, 
 and add [gofail terms](#gofail-term) via the endpoint afterwards. See example below,
 ```
@@ -56,6 +61,11 @@ $ GOFAIL_HTTP="127.0.0.1:22381 ./cmd
 $ curl http://127.0.0.1:22381/my/package/path/SomeFuncString -XPUT -d'sleep("600s")'
 ```
 
+Similarly, you can set multiple failpoints using endpoint `/failpoints`,
+```
+curl http://127.0.0.1:22381/failpoints -X PUT -d'failpoint1=return("hello");failpoint2=sleep(10)'
+```
+
 ## Generated code
 ### Overview
 `gofail enable <optional_file_or_dir_list>` makes the following two changes for each provided go source file, which contains the "gofail" comments,