Update install instructions

[carissableker]

Hi,

I've made a few small changes to allow installing the dependencies with conda easier.

The changes are:

• Update the conda environment file.
  The existing file included many OS dependent libraries and pinned build versions. This makes it very specific to the platform the file was created on. I removed these, and only include the explicit dependencies, so that it can work on different architecture/OS/platforms (cf https://stackoverflow.com/a/39299669/4996681)
• Added missing python library dependencies to the README
• Updated the install instructions (including the use of conda to install the dependencies and the git clone command)
• Changed how the phasiHunter bash script identifies the phasiHunter bin directory, so that is also works if phasiHunter is symlinked instead of being added to the $PATH