Added README.

README.md

+# Trie implementation using nested dictionaries
+This library provides a [trie](https://en.wikipedia.org/wiki/Trie)
+implementation using nested dictionaries. Apart from the basic operations, a
+number of functions for *approximate matching* are implemented.
+
+## Installation
+Via [pypi](https://pypi.python.org/pypi/dict-trie):
+
+    pip install dict-trie
+
+From source:
+
+    git clone https://git.lumc.nl/j.f.j.laros/dict-trie.git
+    cd dict-trie
+    pip install .
+
+## Usage
+The library provides the `Trie` class. Full documentation can be found
+[here](https://git.lumc.nl/j.f.j.laros/dict-trie)
+
+### Basic operations
+Initialisation of the trie is done via the constructor by providing a list of
+words.
+```python
+>>> from dict_trie import Trie
+>>>
+>>> trie = Trie(['abc', 'te', 'test'])
+```
+
+Alternatively, an empty trie can be made to which words can be added with the
+`add` function.
+```python
+>>> trie = Trie()
+>>> trie.add('abc')
+>>> trie.add('te')
+>>> trie.add('test')
+```
+
+Membership can be tested with the `in` statement.
+```python
+>>> 'abc' in trie
+True
+```
+
+Test whether a prefix is present by using the `has_prefix` function.
+```python
+>>> trie.has_prefix('ab')
+True
+```
+
+Remove a word from the trie with the `remove` function. This function returns
+`False` if the word was not in the trie.
+```python
+>>> trie.remove('abc')
+True
+>>> 'abc' in trie
+False
+>>> trie.remove('abc')
+False
+```
+
+Iterate over all words in a trie.
+```python
+>>> list(trie)
+['abc', 'te', 'test']
+```
+
+### Approximate matching
+A trie can be used to efficiently find a word that is similar to a query word.
+This is implemented via a number of functions that search for a word, allowing
+a given number of mismatches. These functions are divided in two families, one
+using the Hamming distance which only allows substitutions, the other using the
+Levenshtein distance which allows substitutions, insertions and deletions.
+
+To find a word that has at most Hamming distance 2 to the word 'abe', the
+`hamming` function is used.
+```python
+>>> trie = Trie(['abc', 'aaa', 'ccc'])
+>>> trie.hamming('abe', 2)
+'aaa'
+```
+
+To get all words that have at most Hamming distance 2 to the word 'abe', the
+`all_hamming` function is used. This function returns a generator.
+```python
+>>> list(trie.all_hamming('abe', 2))
+['aaa', 'abc']
+```
+
+In order to find a word that is closest to the query word, the `best_hamming`
+function is used. In this case a word with distance 1 is returned.
+```python
+>>> trie.best_hamming('abe', 2)
+'abc'
+```
+
+The functions `levenshtein`, `all_levenshtein` and `best_levenshtein` are used
+in a similar way.
+
+### Other functionalities
+A trie can be populated with all words of a fixed length over an alphabet by
+using the `fill` function.
+```python
+>>> trie = Trie()
+>>> trie.fill(('a', 'b'), 2)
+>>> list(trie)
+['aa', 'ab', 'ba', 'bb']
+```
+
+The trie data structure can be accessed via the `root` member variable.
+```python
+>>> trie.root
+{'a': {'a': {'': {}}, 'b': {'': {}}}, 'b': {'a': {'': {}}, 'b': {'': {}}}}
+>>> trie.root.keys()
+['a', 'b']
+```