Documentation: <insert-descriptive-title>:vignettes>description mistake

[XanUniv]

Issue Description

Dear editor,
in seurat->vignettes->PBMC3K-guided tutorial ->Finding differentially expressed features (cluster biomarkers)->heatmap part, there's a mistake in the description ,
the text describes:
DoHeatmap() generates an expression heatmap for given cells and features. In this case, we are plotting the top 20 markers (or all markers if less than 20) for each cluster.
however while the code writes:

pbmc.markers %>%
    group_by(cluster) %>%
    dplyr::filter(avg_log2FC > 1) %>%
    slice_head(n = 10) %>%
    ungroup() -> top10
DoHeatmap(pbmc, features = top10$gene) + NoLegend()

The text tells us that we extract 20 markers in each cluster,but the code shows we only take 10 of them.
It needs to be fixed.