README: improve build instructions and add some building tips

README.md

@@ -15,10 +15,10 @@ gradle wrapper.
 
 Once you have checked out the version you wish to build, run:
 
-```
         cd F-Droid
-gradle clean assembleRelease
-```
+        gradle assembleRelease
+
+The resulting apk will be in `build/outputs/apk/`.
 
 Android Studio
 --------------
@@ -26,6 +26,13 @@ Android Studio
 From Android Studio: File -> Import Project -> Select the cloned top folder
 
 
+Building tips
+-------------
+
+* Use `gradle --daemon` if you are going to build F-Droid multiple times.
+* If you get a message like `Could not find com.android.support:support-...`,
+  make sure that you have the latest Android support maven repository
+
 Direct download
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