refactored documentation

[sneak]

• consolidated unix build instructions
• factored seednodes out into parseable text file
• cleaned up frontpage repo /README.md for clarity
• added docker quickstart examples
• wrapped markdown lines to reasonable width

[sneak]

@steemit/steem-develop-committers ping

[theoreticalbts]

These nodes were removed by the refactoring:

pharesim         78.46.32.4               steemd.pharesim.me (Falkenstein, German)
steemd.pharesim.me:2001

De-duplicate these nodes which are listed multiple times in the node list:

52.4.250.181:39705      # unknown
52.4.250.181:39705      # lafona
81.89.101.133:2001      # unknown
81.89.101.133:2001      # cyrano.witness (Jena, Germany)

We also need to figure out if we really want to use this Docker as an official binary build.

[theoreticalbts]

Updated some commits, after some internal discussion we decided to go with it as far as binary builds

[sneak]

@theoreticalbts if you're happy with seednodes.txt for now please approve and merge

[theoreticalbts]

@mvandeberg can you review this and merge if it's acceptable? I worked on this, so I don't want to be the one to do the final review

[mvandeberg]

Looks good