ARROW-3883: [Rust] Update README
ARROW-3883: [Rust] Update README

Author: Andy Grove <andygrove73@gmail.com>

Closes #3105 from andygrove/ARROW-3883 and squashes the following commits:

e01383548 <Andy Grove> update README

laurentgo/arrow,icexelloss/arrow,itaiin/arrow,xhochy/arrow,icexelloss/arrow,xhochy/arrow,laurentgo/arrow,renesugar/arrow,laurentgo/arrow,renesugar/arrow,itaiin/arrow,icexelloss/arrow,tebeka/arrow,xhochy/arrow,wesm/arrow,laurentgo/arrow,tebeka/arrow,majetideepak/arrow,itaiin/arrow,xhochy/arrow,icexelloss/arrow,pcmoritz/arrow,xhochy/arrow,tebeka/arrow,wesm/arrow,icexelloss/arrow,majetideepak/arrow,tebeka/arrow,tebeka/arrow,renesugar/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,tebeka/arrow,cpcloud/arrow,wesm/arrow,cpcloud/arrow,renesugar/arrow,xhochy/arrow,cpcloud/arrow,majetideepak/arrow,cpcloud/arrow,wesm/arrow,tebeka/arrow,apache/arrow,renesugar/arrow,kou/arrow,laurentgo/arrow,laurentgo/arrow,itaiin/arrow,pcmoritz/arrow,kou/arrow,itaiin/arrow,renesugar/arrow,laurentgo/arrow,majetideepak/arrow,pcmoritz/arrow,itaiin/arrow,xhochy/arrow,apache/arrow,pcmoritz/arrow,pcmoritz/arrow,icexelloss/arrow,itaiin/arrow,majetideepak/arrow,renesugar/arrow,icexelloss/arrow,kou/arrow,itaiin/arrow,pcmoritz/arrow,laurentgo/arrow,itaiin/arrow,pcmoritz/arrow,xhochy/arrow,cpcloud/arrow,cpcloud/arrow,apache/arrow,wesm/arrow,cpcloud/arrow,wesm/arrow,majetideepak/arrow,renesugar/arrow,majetideepak/arrow,wesm/arrow,kou/arrow,apache/arrow,majetideepak/arrow,wesm/arrow,pcmoritz/arrow,apache/arrow,apache/arrow,apache/arrow,icexelloss/arrow,laurentgo/arrow,pcmoritz/arrow,laurentgo/arrow,wesm/arrow,pcmoritz/arrow,itaiin/arrow,renesugar/arrow,cpcloud/arrow,apache/arrow,laurentgo/arrow,xhochy/arrow,cpcloud/arrow,kou/arrow,itaiin/arrow,itaiin/arrow,majetideepak/arrow,apache/arrow,xhochy/arrow,tebeka/arrow,apache/arrow,majetideepak/arrow,cpcloud/arrow,pcmoritz/arrow,itaiin/arrow,renesugar/arrow,apache/arrow,icexelloss/arrow,laurentgo/arrow,pcmoritz/arrow,majetideepak/arrow,wesm/arrow,kou/arrow,icexelloss/arrow,renesugar/arrow,icexelloss/arrow,cpcloud/arrow,majetideepak/arrow,wesm/arrow,kou/arrow,renesugar/arrow,xhochy/arrow,kou/arrow,itaiin/arrow,icexelloss/arrow,laurentgo/arrow,xhochy/arrow,pcmoritz/arrow,majetideepak/arrow,renesugar/arrow,kou/arrow,itaiin/arrow,cpcloud/arrow,icexelloss/arrow,kou/arrow,xhochy/arrow,majetideepak/arrow,tebeka/arrow,renesugar/arrow,laurentgo/arrow,cpcloud/arrow,kou/arrow,cpcloud/arrow,renesugar/arrow,kou/arrow,pcmoritz/arrow,kou/arrow,icexelloss/arrow,xhochy/arrow,tebeka/arrow,majetideepak/arrow,kou/arrow,wesm/arrow,apache/arrow,apache/arrow,apache/arrow,pcmoritz/arrow,xhochy/arrow