corrected and completed gitsigns cheatsheet

[alexander-gabriel]

## gitsigns @git
Next hunk                                | ]c
Previous hunk                            | [c
Stage hunk                               | <leader>hs
Undo stage hunk                          | <leader>hu
Reset hunk                               | <leader>hr
Preview hunk                             | <leader>hp
Stage buffer                             | <leader>hS
Reset buffer                             | <leader>hR
Blame current line                       | <leader>hb
Toggle blame current line                | <leader>tb
Diff this                                | <leader>hd
Diff home                                | <leader>hD
Toggle show deleted                      | <leader>td
Hunk text object                         | ih