Update index.md

[squenson1]

Make the spelling of "indegree" consistent:
"in-degree" --> "indegree"

[dschult]

Consistent with what? What are you matching with?

[squenson1]

"Consistent" meaning one spelling or the other, not both in such a short text, it is very confusing (even if both seems to be accepted in the literature).

[rossbar]

FWIW I think we should actually go the opposite direction, i.e. "indegree" -> "in-degree". The reason being consistency with NetworkX itself, which clearly favors the latter spelling. You can verify this with grep:

# In the networkx source repo
$ grep -rIo "indegree" | wc -l
30
$ grep -rIo "in-degree" | wc -l
58

All of the instances of indegree are variable names in code, so in-degree is the clear winner for documentation!

[squenson1]

Fine for me, one spelling or the other but not both!

[rossbar]

LGTM, thanks @squenson1 !