Miscellaneous iam.py docstring updates (#2251)

* Update iam.py

* restore comment

* remove blank line

* Update iam.py

* sorry for the rapid commit spam

* Apply suggestions from code review

Co-authored-by: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>

---------

Co-authored-by: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>

Author: RDaxini

pvlib/iam.py

@@ -269,8 +269,8 @@ def martin_ruiz(aoi, a_r=0.16):
 
     which is presented as :math:`AL(\alpha) = 1 - IAM` in equation 4 of [1]_,
     with :math:`\alpha` representing the angle of incidence AOI. Thus IAM = 1
-    at AOI = 0, and IAM = 0 at AOI = 90.  This equation is only valid for
-    -90 <= aoi <= 90, therefore `iam` is constrained to 0.0 outside this
+    at AOI = 0°, and IAM = 0 at AOI = 90°.  This equation is only valid for
+    0° <= aoi <= 90°, therefore `iam` is constrained to 0.0 outside this
     interval.
 
     References
@@ -891,8 +891,8 @@ def schlick_diffuse(surface_tilt):
     implements only the integrated Schlick approximation.
 
     Note also that the output of this function (which is an exact integration)
-    can be compared with the output of :py:func:`marion_diffuse` which numerically
-    integrates the Schlick approximation:
+    can be compared with the output of :py:func:`marion_diffuse` which
+    numerically integrates the Schlick approximation:
 
     .. code::