update readme for 2021.03 version

Dockerfile

@@ -94,5 +94,3 @@ RUN go get golang.org/x/mobile/cmd/gobind
 RUN go get golang.org/x/mobile/bind
 
 RUN gomobile clean
-# RUN gomobile init
-

README.md

@@ -13,20 +13,21 @@ Versions are:
 
 ## Install and Use
 
-### Version 2018.07
+### Version 2021.03
 
 This image includes:
 
-- Android SDK, NDK, tools, and API version 28 at `/usr/local/android-sdk`
+- Android SDK, NDK, tools, and API version 29 and Buildtools 30.0.2 at `/usr/local/android-sdk`
 - Go lang 1.10.3 at `/usr/local/go`
-- $GOPATH set to `/workspace/go`
-- A go directory with an initialized gomobile installed at `/go`
+- $GOPATH set to `/gomobile`
+	- GOPATH includes gomobile cmd tools and source
 
-This image comes with gomobile checkedout and preinitialized (time and space consuming). In order to install this predone work from the image into your Drone CI workspace (a docker volume mounted to `/workspace`), you will want your first pipeline step to be:
+This container has its own GOPATH with only gomobile in it, so to use, you'll need to re-get your go dependancies and then run `gomobile init`.  The following example shows a Drone CI step using this image
 
-    go-link:
-      image: openpriv/android-go-mobile
+    gomobile-build:
+      image: openpriv/android-go-mobile:2021.03
       commands:
-        - cp -as /go /workspace/go
+        - go mod download
+	- gomobile init
+	- make
 
-`cp -as` recreates the directory structure from /go in /workspace/go but for each file, it just creates a symlink. This is the quickest and most efficent way to mirror the work supplied with the image into your workspace.