tcollector: add source code URL, license, language, update description

- ref. https://github.com/awesome-foss/awesome-sysadmin/issues/416

README.md

@@ -542,7 +542,7 @@ _See also: [Databases](#databases)_
 - [Graphite](https://graphite.readthedocs.org/en/latest/) - Scalable graphing server. ([Source Code](https://github.com/graphite-project/graphite-web)) `Apache-2.0` `Python`
 - [RRDtool](https://oss.oetiker.ch/rrdtool/) - Industry standard, high performance data logging and graphing system for time series data. ([Source Code](https://github.com/oetiker/rrdtool-1.x)) `GPL-2.0` `C`
 - [Statsd](https://github.com/etsy/statsd/) - Daemon that listens for statistics like counters and timers, sent over UDP or TCP, and sends aggregates to one or more pluggable backend services. `Nodejs` `MIT`
-- [tcollector](http://opentsdb.net/docs/build/html/user_guide/utilities/tcollector.html) - System statistic collection daemon written in Python for OpenTSDB
+- [tcollector](http://opentsdb.net/docs/build/html/user_guide/utilities/tcollector.html) - Gathers data from local collectors and pushes the data to OpenTSDB. ([Source Code](https://github.com/OpenTSDB/tcollector/)) `LGPL-3.0/GPL-3.0` `Python`
 - [Telegraf](https://github.com/influxdata/telegraf) - The plugin-driven server agent for collecting & reporting metrics.