Add the needed space in the welcome message

[echarles]

Ensure the needed space is present between communityand resources to fix the following welcome message.

` in contributing to the platform, please visit the communityresources section at https://jupyter.org/community.html``

[codecov-commenter]

Codecov Report

Merging #561 (3274aa0) into master (7d2f04f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #561   +/-   ##
=======================================
  Coverage   76.93%   76.93%           
=======================================
  Files         109      109           
  Lines        9948     9948           
  Branches     1078     1078           
=======================================
  Hits         7653     7653           
  Misses       1913     1913           
  Partials      382      382           

Impacted Files	Coverage Δ
jupyter_server/serverapp.py	66.10% <ø> (ø)

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