Adds welcome bot config and code of conduct

[codecov-commenter]

Codecov Report

Merging #70 (5c6cb1a) into master (bc6687c) will decrease coverage by 2.13%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #70      +/-   ##
==========================================
- Coverage   81.30%   79.16%   -2.14%     
==========================================
  Files           8        8              
  Lines         230      240      +10     
==========================================
+ Hits          187      190       +3     
- Misses         43       50       +7     

Impacted Files	Coverage Δ
datalad_xnat/init.py	67.21% <0.00%> (-4.22%)	:arrow_down:
datalad_xnat/platform.py	76.92% <0.00%> (-3.08%)	:arrow_down:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update bc6687c...5c6cb1a. Read the comment docs.

[adswa]

thank you!