DOC, MAINT: update 1.5.1 relnotes

* update the SciPy `1.5.1` release notes
to reflect the PRs backported so far

doc/release/1.5.1-notes.rst

@@ -12,11 +12,36 @@ fixed.
 Authors
 =======
 
+* Peter Bell
+* Loïc Estève
+* Philipp Thölke +
+* Tyler Reddy
+* Paul van Mulbregt
+* Pauli Virtanen
+* Warren Weckesser
+
+A total of 7 people contributed to this release.
+People with a "+" by their names contributed a patch for the first time.
+This list of names is automatically generated, and may not be fully complete.
+
 
 Issues closed for 1.5.1
 -----------------------
 
+* `#9108 <https://github.com/scipy/scipy/issues/9108>`__: documentation: scipy.spatial.KDTree vs. scipy.spatial.cKDTree
+* `#12218 <https://github.com/scipy/scipy/issues/12218>`__: Type error in stats.ks_2samp when alternative != 'two-sided-
+* `#12406 <https://github.com/scipy/scipy/issues/12406>`__: DOC: Docstring in stats.anderson function not properly formatted
+* `#12418 <https://github.com/scipy/scipy/issues/12418>`__: Regression in hierarchy.dendogram
+
 
 Pull requests for 1.5.1
 -----------------------
 
+* `#12280 <https://github.com/scipy/scipy/pull/12280>`__: BUG: Fixes gh-12218, TypeError converting int to float inside...
+* `#12336 <https://github.com/scipy/scipy/pull/12336>`__: BUG: KDTree should reject complex input points
+* `#12344 <https://github.com/scipy/scipy/pull/12344>`__: MAINT: Don't use numpy's aliases of Python builtin objects.
+* `#12407 <https://github.com/scipy/scipy/pull/12407>`__: DOC: Fix docstring for dist param in anderson function
+* `#12410 <https://github.com/scipy/scipy/pull/12410>`__: CI: Run the Azure Windows Python36 32bit tests with mode 'fast'
+* `#12421 <https://github.com/scipy/scipy/pull/12421>`__: Fix regression in scipy 1.5.0 in dendogram when labels is a numpy...
+* `#12462 <https://github.com/scipy/scipy/pull/12462>`__: MAINT: move distributor_init import after __config__ import
+