help: add help entry for internals.mergestate
This patch adds an entry for `internals.mergestate` as suggested
by @marmoute. Most of the help text is taken from `merge.mergestate`.
Differential Revision: https://phab.mercurial-scm.org/D6448
Differential Revision: https://phab.mercurial-scm.org/D6528
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2