Add nix to the supported ecosystems in the README #201

Signed-off-by: Chin Yeung Li <tli@nexb.com>

Author: chinyeungli

README.rst

@@ -89,6 +89,7 @@ Ecosystems supported for fetching a purl from fetchcode:
 - hex
 - luarocks
 - maven
+- nix
 - npm
 - nuget
 - pub
@@ -110,19 +111,19 @@ This project is funded, supported and sponsored by:
 
 - Generous support and contributions from users like you!
 - the European Commission NGI programme
-- the NLnet Foundation 
+- the NLnet Foundation
 - the Swiss State Secretariat for Education, Research and Innovation (SERI)
 - Google, including the Google Summer of Code and the Google Seasons of Doc programmes
 - Mercedes-Benz Group
 - Microsoft and Microsoft Azure
 - AboutCode ASBL
-- nexB Inc. 
+- nexB Inc.
 
 
 
-|europa|   |dgconnect| 
+|europa|   |dgconnect|
 
-|ngi|   |nlnet|   
+|ngi|   |nlnet|
 
 |aboutcode|  |nexb|
 
@@ -136,7 +137,7 @@ Communications Networks, Content and Technology under grant agreement No 1010929
 
 This project was funded through the NGI0 Entrust Fund, a fund established by NLnet with financial
 support from the European Commission's Next Generation Internet programme, under the aegis of DG
-Communications Networks, Content and Technology under grant agreement No 101069594. 
+Communications Networks, Content and Technology under grant agreement No 101069594.
 
 |ngizeroentrust| https://nlnet.nl/project/Back2source/
 
@@ -150,7 +151,7 @@ Communications Networks, Content and Technology under grant agreement No 1010929
 
 This project was funded through the NGI0 Entrust Fund, a fund established by NLnet with financial
 support from the European Commission's Next Generation Internet programme, under the aegis of DG
-Communications Networks, Content and Technology under grant agreement No 101069594. 
+Communications Networks, Content and Technology under grant agreement No 101069594.
 
 |ngizeroentrust| https://nlnet.nl/project/purl2all/