docs(readme) update fork description (#3)

We still have to figure out if this needs to be fixed in the module
itself or not. In the meantime, remove wording that makes it sound like
the problem is in the SDK.

Author: thibaultcha

README.md

@@ -1,11 +1,8 @@
 # WebAssembly for Proxies (AssemblyScript SDK)
 
 This is a friendly fork of https://github.com/solo-io/proxy-runtime/,
-temporarily mantained to address one incompatibility between the SDK and
-ngx_wasm_module.
-
-This fork should no longer be needed once that is handled in the upstream.
-
+temporarily mantained to address an incompatibility between the AssemblyScript
+SDK and ngx_wasm_module.
 
 ## How to use this SDK