hledger-*: add pages for seven hledger subcommands (#12828)

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: Juri Dispan <juri.dispan@posteo.net>
Co-authored-by: spageektti <git@spageektti.cc>

pages/common/hledger-incomestatement.md

@@ -0,0 +1,20 @@
+# hledger incomestatement
+
+> Show revenue inflows and expense outflows during the report period.
+> More information: <https://hledger.org/hledger.html#incomestatement>.
+
+- Show revenues and expenses (changes in Revenue and Expense accounts):
+
+`hledger incomestatement`
+
+- Show revenues and expenses each month:
+
+`hledger incomestatement --monthly`
+
+- Show monthly revenues/expenses/totals, largest first, summarised to 2 levels:
+
+`hledger incomestatement --monthly --row-total --average --sort --depth 2`
+
+- Short form of the above, and generate HTML output in `is.html`:
+
+`hledger is -MTAS -2 -o is.html`