Update README.md

[leonarddt05]

Hello,

I suggest two changes for this section:

First one is a mistyped word: "phases" should be "phrases" in the sentence: "- fill the mnemonic phases of your account in truffle.js"

Second one is a grammatical suggestion: In the sentence: "- get some ethers from rinkeby/ropsten faucet.", "ethers" can be written as "Ether" for better readability.

Thanks.