Add release and milestone information to Readme (#2401)
Add release and milestone information to Readme (#2401)

* Add release and milestone information to Readme

* Readme updates in response to comments

google/blockly,nickmain/blockly,rachel-fenichel/blockly,google/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,joshlory/blockly,rachel-fenichel/blockly,nickmain/blockly,google/blockly,joshlory/blockly,nickmain/blockly,mark-friedman/blockly,nickmain/blockly,mark-friedman/blockly,rachel-fenichel/blockly,mark-friedman/blockly,nickmain/blockly,joshlory/blockly,mark-friedman/blockly,rachel-fenichel/blockly,google/blockly,nickmain/blockly,google/blockly,rachel-fenichel/blockly,picklesrus/blockly,google/blockly,picklesrus/blockly,google/blockly,mark-friedman/blockly,picklesrus/blockly,mark-friedman/blockly