added appium beta install doc

install-beta.md

@@ -0,0 +1,32 @@
+#appium beta install
+
+## global install
+
+Install with:
+
+```
+npm install -g appium@beta
+```
+
+Start with:
+
+```
+appium
+```
+
+## local install
+
+Install with:
+
+```
+mkdir beta
+cd beta
+npm init # press <Enter when asked>
+npm install appium@beta
+```
+
+Start with
+```
+"node_modules/.bin/appium"
+```
+