Fill up the missing docs for Index/MultiIndex (#1123)

as commented in #1114 (comment),

i filled up the missing docs for `Index` and `MultiIndex`

docs/source/reference/indexing.rst

@@ -18,11 +18,18 @@ Properties
 .. autosummary::
    :toctree: api/
 
+   Index.is_monotonic
+   Index.is_monotonic_increasing
+   Index.is_monotonic_decreasing
+   Index.has_duplicates
+   Index.hasnans
    Index.dtype
    Index.shape
    Index.name
    Index.names
    Index.ndim
+   Index.size
+   Index.nlevels
    Index.empty
    Index.T
 
@@ -32,6 +39,8 @@ Modifying and computations
 .. autosummary::
    :toctree: api/
 
+   Index.all
+   Index.any
    Index.copy
    Index.is_boolean
    Index.is_categorical
@@ -42,6 +51,8 @@ Modifying and computations
    Index.is_object
    Index.min
    Index.max
+   Index.rename
+   Index.unique
    Index.value_counts
 
 Missing Values
@@ -63,7 +74,12 @@ Conversion
    Index.to_series
    Index.to_numpy
 
-.. _api.multiindex:
+Time-specific operations
+~~~~~~~~~~~~~~~~~~~~~~~~
+.. autosummary::
+   :toctree: api/
+
+   Index.shift
 
 Combining / joining / set operations
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -79,6 +95,8 @@ Selecting
 
    Index.isin
 
+.. _api.multiindex:
+
 MultiIndex
 ----------
 .. autosummary::
@@ -91,17 +109,22 @@ MultiIndex Constructors
 .. autosummary::
    :toctree: api/
 
+   MultiIndex.from_arrays
    MultiIndex.from_tuples
 
 MultiIndex Properties
 ~~~~~~~~~~~~~~~~~~~~~
 .. autosummary::
    :toctree: api/
 
+   MultiIndex.has_duplicates
+   MultiIndex.hasnans
    MultiIndex.shape
    MultiIndex.names
    MultiIndex.ndim
+   MultiIndex.empty
    MultiIndex.T
+   MultiIndex.size
    MultiIndex.nlevels
    MultiIndex.levshape
 
@@ -110,6 +133,7 @@ MultiIndex Missing Values
 .. autosummary::
    :toctree: api/
 
+   MultiIndex.fillna
    MultiIndex.dropna
 
 MultiIndex Modifying and computations
@@ -118,6 +142,8 @@ MultiIndex Modifying and computations
    :toctree: api/
 
    MultiIndex.copy
+   MultiIndex.min
+   MultiIndex.max
    MultiIndex.value_counts
 
 MultiIndex Combining / joining / set operations
@@ -127,9 +153,10 @@ MultiIndex Combining / joining / set operations
 
    MultiIndex.symmetric_difference
 
-Conversion
-~~~~~~~~~~
+MultiIndex Conversion
+~~~~~~~~~~~~~~~~~~~~~
 .. autosummary::
    :toctree: api/
 
+   MultiIndex.astype
    MultiIndex.to_numpy