Updates gominer README with build instructions for mac, updated link …

[s-ben]

This is the result of my journey building gominer from source for mac, getting it working, and seeing some doc improvements that will (hopefully) be helpful.

Makes the below updates/tweaks.

• Adds build instructions for Mac. I was able to build gominer for Mac, using the Linux instructions as is, so have just copied them into a new Mac section. Note: because I had NVIDIA CUDA installed already, I wasn't able to test the Linux example instruction (sudo apt-get install beignet-dev nvidia-cuda-dev nvidia-cuda-toolkit). So I just left the high-level instruction to do so. Also, I was able to successfully build the Go files using the same command as Linux: go build -tags opencl. However, I was not able to test the other two options (make and go build -tags opencladl). Assuming these will work on mac as well.

• Updates binaries link to the last release gominer binaries were released with (v1.0.0).

• Adds reference to ASICs in description, as gominer will also work with ASICs.

• Made note on pool mining example command (that you must append a worker name to username for some pools (an issue that tripped me up and caused me to need help in #pow_mining).

• Minor formatting/flow tweaks

[jcvernaleo]

@dajohi My reviews don't count any more but I think this looks good and you should merge it in.

[dajohi]

@s-ben please update README to handle go 1.11. (remove dep, for instance)

[s-ben]

@dajohi , it looks like you updated the README for Linux yesterday; don't see any remaining references to dep. So I just added a general paragraph (below) about modules being added. Got this text from the Politeia README and lightly edited it. I googled a bit looking for equivalent instructions on windows, but didn't find anything...presumably Windows users can figure that out with a heads up at the top of the build instructions.

NOTE: Go 1.11 introduced modules, a new dependency management approach, that obviates the need for third party tooling such as dep.

Usage is simple and nothing is required except Go 1.11. If building in a folder under GOPATH, it is necessary to explicitly build with modules enabled. For Linux installations, this is implemented in the build commands below. For more information on this requirement, see the How to Use Modules page on the Go wiki.

P.S. My rebase with the latest changes got a bit messy. Might want to double check that I didn't screw up any recent changes.