Update README.md with common issues encountered when building on Ubuntu
diff --git a/sflphone-android/.gitignore b/sflphone-android/.gitignore
index 0a64b7c..d00a811 100644
--- a/sflphone-android/.gitignore
+++ b/sflphone-android/.gitignore
@@ -38,6 +38,7 @@
 StringMap.java
 StringVect.java
 IntVect.java
+IntegerMap.java
 Callback.java
 VectMap.java
 *.o