Update magicleap README for SDK 0.20.0
# Magic Leap demo
-First, install the Magic Leap SDK. By default this is installed in `MagicLeap/mlsdk/<version>`, for example:
+First, install v0.20.0 or later of the Magic Leap SDK. By default this is installed in `MagicLeap/mlsdk/<version>`, for example:
```
- export MAGICLEAP_SDK=~/MagicLeap/mlsdk/v0.19.0
+ export MAGICLEAP_SDK=~/MagicLeap/mlsdk/v0.20.0
```
You will also need a signing certificate.
```
