Update 6.9-to-7.0.md

fix gitlab.yml example diff command
Text changes to projects API documentation

Fixes some grammar / punctuation errors and inconsistencies.
Fixed typos in Development - Rake Tasks doc
Merge pull request #7411 from robbytaylor/patch-3

Fixed typos in Development - Rake Tasks doc
Merge pull request #7410 from robbytaylor/patch-1

Text changes to projects API documentation
Merge pull request #7201 from nacengineer/patch-2

Update 6.9-to-7.0.md
Replace invalid emojis
Mention the @all GFM reference
Merge pull request #7419 from Razer6/fix_emoji

[DOC] Replace invalid emojis
Merge pull request #7420 from Razer6/mention_all_markup

[DOC] Mention the @all GFM reference in documentation
Remove GitLab user
Self signed SSL cert not supported until 5.1
add command to start rails console
Merge pull request #7421 from bbodenmiller/self-signed-cert-note

Self signed SSL cert not supported until 5.1
Merge pull request #7424 from bbodenmiller/patch-1

add command to start rails console
Merge pull request #7422 from bbodenmiller/rm-gitlab-user

Add command to remove GitLab user
Merge branch 'simplify-ssl-setup' into 'master'

Simplify ssl setup

/cc @dzaporozhets

Fixes #1409

See merge request !1006
Merge branch 'master' of github.com:gitlabhq/gitlabhq
add application check commands
make bullet punctuation consistent