Clean up default data directory and flesh out README

* Removed compiled_view folder and its README; ThinkUp will create it as needed

.gitignore

@@ -1,6 +1,6 @@
 webapp/config.inc.php
 webapp/config.inc.bak.php
-webapp/data/*
+webapp/data/
 data/
 tests/config.tests.inc.php
 .*

webapp/data/README.md

@@ -1,3 +1,9 @@
-This is the default ThinkUp data directory, which can be changed via $THINKUP_CFG['datadir_path']
+This is the ThinkUp data directory. Its path is set and may be changed in config.inc.php's
+$THINKUP_CFG['datadir_path'] value.
 
-Whichever directory used must be read-writable by the user the web server is running as.
+For ThinkUp to function, this directory must be read-writable by the web server user. ThinkUp automatically creates
+files and folders inside this folder to store data while performing functions which require file storage.
+
+More information:
+
+http://thinkupapp.com/docs/install/perms.html