remove mention of num_vertices and num_edges in the documentation

[etiennedeg]

fix#168

[codecov]

Codecov Report

Merging #169 (4484ca3) into master (b2a5b0b) will decrease coverage by 0.34%.
The diff coverage is 0.00%.

@@ Coverage Diff @@## master #169 +/- ##
==========================================
- Coverage 33.26% 32.92% -0.35% 
==========================================
Files 9 9 Lines 526 565 +39 ==========================================
+ Hits 175 186 +11 - Misses 351 379 +28 

Impacted Files	Coverage Δ
src/GraphPlot.jl	100.00% <ø> (ø)
src/collapse_plot.jl	0.00% <0.00%> (ø)
src/deprecations.jl	0.00% <0.00%> (ø)
src/layout.jl	48.42% <0.00%> (+1.75%)	⬆️
src/lines.jl	52.22% <0.00%> (-0.12%)	⬇️
src/stress.jl	0.00% <0.00%> (ø)
src/pienode.jl	0.00% <0.00%> (ø)
src/plot.jl	62.63% <0.00%> (+0.56%)	⬆️
... and 1 more

---

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 9e734d5...4484ca3. Read the comment docs.

[etiennedeg]

I merge since this is only doc and should not be controversial.