Update README.md

Author: ciquLi

README.md

@@ -1,25 +1,25 @@
 # fast_ip2as
-Fast and accurate ip2as.
+Fast Mapping database generation and ip-to-AS mapping.
 
 The ip2as mapping is accomplished by pyasn (https://github.com/hadiasghari/pyasn.git).
 
 In this repository, we just provide a faster and more convenient way to obtain the mapping database. We use the routeviews Prefix-to-AS mappings (pfx2as) for IPv4 and IPv6 provided by CAIDA to generate the database. 
 
 You can download the pfx2as files from https://publicdata.caida.org/datasets/routing/routeviews-prefix2as/
 
-Steps:
+# Steps:
 
 1. install 
   pip install pyasn
 2. Download pfx2as file from CAIDA
 3. Generate the mapping db file
 4. Usage
 
-  import pyasn
-  
-  asndb = pyasn.pyasn('ipasn.dat')
-  
-  asndb.lookup('8.8.8.8')  # should return: (15169, '8.8.8.0/24'), the origin AS, and the BGP prefix it matches
-  
-  asndb.get_as_prefixes(1128) # returns ['130.161.0.0/16', '131.180.0.0/16', '145.94.0.0/16'], TU-Delft prefixes
+    import pyasn
+
+    asndb = pyasn.pyasn('ipasn.dat')
+
+    asndb.lookup('8.8.8.8')  # should return: (15169, '8.8.8.0/24'), the origin AS, and the BGP prefix it matches
+
+    asndb.get_as_prefixes(1128) # returns ['130.161.0.0/16', '131.180.0.0/16', '145.94.0.0/16'], TU-Delft prefixes