docs: list all six experiment adapters in README (#16)

memory, cpu, and network adapters were added but never added to the
adapter list.

Signed-off-by: Akanksha Trehun <akankshatrehun@gmail.com>

Author: magic-peach

README.md

@@ -150,8 +150,8 @@ experiments:
           snapshotter: devmapper
 ```
 
-The available experiment adapters are `lifecycle`, `storage`, and
-`http-readiness`.
+The available experiment adapters are `lifecycle`, `storage`,
+`http-readiness`, `memory`, `cpu`, and `network`.
 
 For HTTP readiness, specify the nginx image and an available host port. The
 adapter pulls and creates the container before measurement, then starts a GET