Fix misleading stuff about HTML cells on sagenb

[kcrisman]

From sage-support:

The directive given in the help doesn't work: 
Shift click between cells to create a new HTML cell. Double click on 
existing HTML to edit it. 
Use $...$ and $$...$$ to include typeset math in the HTML block. 

There is no mention of the horizontal blue line.

CC: @TimDumol

Component: notebook

Author: Alex Leone

Reviewer: Tim Dumol

Merged: sagenb-0.7

Issue created by migration from https://trac.sagemath.org/ticket/7848

[qed777]

comment:1

Should we move the contents of tutorial.py to an HTML file?

[TimDumol]

comment:2

I believe that some of it can be put into the documentation, under "The Notebook Interface", which is a bit lacking.

[sagetrac-acleone]

Attachment: trac_7848-misleading_HTML_cells.patch.gz

Changes the tutorial help verbage regarding text (HTML) cells. Also replaces all the tags in the tutorial with

[sagetrac-acleone]

comment:3

trac_7848-misleading_HTML_cells.patch: changes verbage to:

Insert New Text Cell

Move the mouse between cells until a blue bar appears.
<strong>Shift-click</strong> on the blue bar to create a new text cell.
Double click on existing text to edit it.
Use $...$ and $$...$$ to include typeset math in the text block.

[TimDumol]

Author: Alex Leone

[TimDumol]

comment:4

LGTM.

[TimDumol]

Reviewer: Tim Dumol