Merge pull request #3 from juleskers/patch-1

Also add file-input example to github-readme

Author: jbaiter

README.md

@@ -70,6 +70,17 @@ m = Map.from_iter(items, path="/tmp/map.fst")
 matches = dict(m['clarence':])
 assert matches == {'clarence': 2, 'stevie': 3}
 
+# Create a map from a file input, using generators/yield
+# The input file must be sorted on the first column, and look roughly like
+#   keyA 123
+#   keyB 456
+def file_iterator(fpath):
+  with open(fpath, 'rt') as fp:
+    for line in fp:
+      key, value = line.strip().split()
+      yield key, int(value)
+m = Map.from_iter( file_iterator('/your/input/file/'), '/your/mmapped/output.fst')
+
 # re-open a file you built previously with from_iter()
 m = Map(path='/path/to/existing.fst')
 ```